Short Answers

Butterfly on a Translucent Leaf
This image nicely illustrates the definition of "translucent". A translucent object (the leaf in this case) allows light to pass through, but some of that light is scattered (so in this case you can't see a clear image of the butterfly on the other side.


So Many Questions ...


During the summer of 2006, Doug Hemink, a high school intern working with us in the Center for Imaging Science, helped me sort through all the submitted questions and come up with candidates for each module. So many wonderful questions were submitted by students around the world, that I just couldn't bring myself to limit the answers to the 64 modules in the main body of the Color Curiosity Shop. So I decided to add this page of short answers to many of the other questions. I hope you have as much fun exploring them as I did collecting and answering them. There are about 200 questions and answers here! Don't forget to scroll all the way down the page (there are some leftover images near the bottom). Some answers have two or more questions attached to them since the questions were so similar. Please use your web browser's "find" feature (usually "command-f") to find key words in questions and answers. I make no promises that my answers are perfect. If you have comments, suggestions, or references to more correct answers, let me know through the feedback page.

If you want even more questions and answers with for more technical detail, visit our lab's Ask a Color Scientist page.

Last Updated: March 25, 2008

Questions and Answers...


Q: Why is color?
A: Why not? Color is a perception that arises from the responses of our visual systems to light in the environment. We probably have evolved with color vision to help us in finding good food and healthy mates. Why it exists, why we perceive it, etc. are the reasons for this website. Explore!

Q: What is color?
A: Color is a perception that depends on the response of the human visual system to light and the interaction of light with objects (the stimulus, sometimes referred to as the color stimulus).

Q: How many colors are there?
Q: How many colors are there in the world?
A: This one is making it to the main resource and is also the topic of my example page that you can download for more details.

Q: Why do leaves change color in the autumn?
A: See this website for starters. And here is a simpler, but perhaps slightly less accurate explanation.

Q: Can the autumn leaf color on a given tree vary from one autumn to the next?
A: Generally no, the color a tree's leaves turn in the autumn is genetically determined. However there can be significant variation due to differences in light exposure, temperature, and water. For example, in the courtyard outside my office there are three essentially identical oak trees. However one is near the south wall (largely shaded), one near the north, and one near the east. One autumn recently, the three trees changes to three distinct colors; yellow, orange, and red. This website has more details.

Q: Why does light produce color?
A: Light produces color because of how our visual systems respond to light with different responses to the various colors in the spectrum. Without our visual system, light can't make color on it's own.

Q: Why are leaves green? Why not black?
A: Here is a website that explains why plants are green. It is interesting, but it really doesn't address the question of why they aren't black. One might think that black leaves would absorb even more sunlight and therefore be able to complete even more photosynthesis. I don't know the answer, but I can certainly speculate as a color scientist. There are two reasons that come to mind that would make green leaves preferable (and thus evolutionarily advantaged) to black leaves. The first is heat. If leaves were black, they would absorb a lot more light, but they would also have to figure out a way to dissipate the extra heat. Many plants wilt and die if they get too hot, so this would limit the areas plants could live. Green plants reflect/transmit the wavelengths were there is the most visible energy, thus keeping them cooler. That also makes them more visible. The second is translucency. If the leaves absorbed all the light, then there would be none transmitted to the leaves below. Every plant would end up being a single layer of leaves. I would suspect that being an imperfect absorber makes it possible for layers upon layers of leaves to effectively survive. I would also think that these layers of leaves that are green are making much more oxygen for us all than a single layer of black leaves could. Lastly, you could simply say that green leaves are more attractive to the animals and humans that interact with them and promote their survival. The question to then ponder is why the flowers and fruits are not green!

Q: How are the colors in fireworks made?
Q: How do fireworks make light and color?
A: This link is a little technical, but I think you will enjoy the explanation. Basically, different chemicals produce different color light emission when they are heated/burned.

Q: How does a television produce color?
Q:How does color get through a TV?
Q: How does color TV work?
A: This is a great question that is also in the main resource. For now, here is a great website describing how TV works.

Q: Do different colors heat up differently?
A: It is hard to say since it depends somewhat on the object and the environment it is in, but in general darker colors heart up faster with exposure to light. So a dark purple will heat up faster than a light green, but a dark green will also heat up faster than a light purple.

Q: What colors do girls like?
A: Whatever they want. There is no intrinsic gender specificity in favorite colors. Anything that does exist is learned from the culture. See the next answer for more details.

Q: Why is pink associated with girls and blue with boys?
A: I had no idea, but I looked it up and found this page. One of our staff scientists confirmed that he had read about similar explanations in the past. Apparently it was pink for boys and blue for girls up until about the time of World War II and the Nazis in Germany caused some of the switch due to a very detailed system of colors used to identify various groups of people. This is one potential source for the switch around that time. Others are also suggested on that page and some that are linked to it. It comes down to a choice in society. It becomes accepted within a society to associate certain colors with certain activities (pink for little girls, white wedding dresses, etc.) and the human nature to want to fit in with your society leads many people to follow these customs until something significant (like World War II) causes a change in the ideas everyone at once.

Q: Is it possible to invent a new color?
A:That is a wonderful and fascinating question. As a color scientist, I think of colors as perceptions, that is things that we see. Of course those perceptions are not just caused by our brain (except when we are dreaming), they are caused by how our eyes and brain respond to the world around us. For color it is the light and objects that we are responding to. Most people would take this question to mean "has anyone invented a light or object of a new color?" Personally, I have not, but I have invented new ways to understand and describe how we perceive and produce colors in places like the movies. Other people certainly have invented new materials that produce colors that people couldn't make before. Things like new paints, new inks, new kinds of televisions. That has happened often through the history of science. But, if we come back to color being a perception, then it is even easier to say that we invent new colors. I think we all do it quite often if we pay attention to the world around us. Have you ever had a time when you looked at something and it seemed like a totally new experience? Maybe a special rainbow, or a peculiar bird, or a strange way the light bounces around your room? If you have noticed a new experience like that, then I think you could say you have invented a new color. That is because color is truly a perception that is unique to you and any new color experiences could be considered "inventions". I like to just think of them as interesting parts of our world that make it fun to study science; in my case color science.

Q: Why do my two eyes seem to perceive color differently?
A: There are a a couple of reasons for this. One is that sometimes there are small physiological differences between the two eyes. This results in our color vision often being slightly different between our two eyes. Also, if you close one eye at a time to make comparisons, a second cause is adaptation. When you go into a dark place, dark adaptation helps your visual system to see better by making your eyes more sensitive to light. The opposite (light adaptation) makes your eyes less sensitive when there is plenty of light. When you close one eye, it is becoming dark adapted (more sensitive) and then when you open it back up all the colors will look brighter.

Q: Why do colors fade in the sun? Is it caused by heat or light?
A: Basically, colors fade because some chemical reaction causes the colorants (the material the produces the color appearance) to change form or breakdown. In the case of fading in the sun, it is the energy from the absorbed sunlight that causes these changes. Both light and heat (absorbed light is converted to heat) can facilitate these processes.

Q: What is your favorite color?
A: That's the easiest one ... Red. Just for fun, there are a lot of studies that show blue is the most popular favorite color. I bet if you ask a bunch of people, blue will get the most votes. Usually red comes in second.

Q: Who invented color?
Q: My psychology professor asked my class who invented color? Who did color originally come from?
A: I would say no-one invented colors. Since colors are perceptions, that would be kind of like asking "who invented people". There are plenty of debates about that, but not usually within color science. Even colorants, the stuff we use to give color to various objects weren't really invented. People used whatever materials they could find to impart color. Long ago, insects were a common source for colorants along with mud, rocks, berries, and other common things. Nowadays, chemical researchers work very hard to make new colorants for various applications.

Q: Do some rocks have bright colors?
A: Definitely! Have you ever seen a beautiful piece of jewelry, or a picture of jewelry. The beautiful colors in jewelry often come from what we call precious stones and stones are just small rocks. Things like sapphires, rubies, and emeralds are all rocks and have very bright colors. There is an interesting one called alexandrite that actually changes in perceived color when the lighting changes!

Q: If no light falls on an object does it still have a color?
A: Color is technically defined as a perception and if there is no light to initiate that perception, then there is no color. So I would say that if there is no light falling on an object it doesn't have a color. If there is light on other objects in the scene, but none on that one particular object, then its color would be black (which is a color).

Q: Does color only exist because we have eyes?
Q: Is color limited to the interaction of light with an object and our eyes?
A: Yes, we need to have our eyes involved to have color but we do a lot of manipulation of lighting and objects to control those color perceptions. There is plenty of color science that just involves the light and objects without worrying about the eye too much. You need light and the eye, but you don't necessarily need an object ... lights can be colored all on their own.

Q: Do insects that have UV sensitivity in their visual system see the UV portion of the spectrum as "color"?
A: It is really impossible to say for sure, but it seems that their visual systems are designed such that the UV part of the spectrum gets processed as another color response. Of course it is possible that they don't see "color" at all and just use the different responses for different functions (sort of different sets of black and white images for different purposes).

Q: Do humans have a natural affinity for certain sorts of colors more than others as compared to other creatures?
A: It is very difficult to say. Our affinity for colors is very much influenced by society, so you could say that we do since our society is different. If there are inherent affinities, then they might well be similar for other animals that have similar visual systems (which turn out to be relatively few in number).

Q: Why do colors have names?
A: Probably just so that we can communicate. If I want to tell you to only eat ripe bananas, I can say "don't eat the bananas until they are yellow". Without the word "yellow" it would be much more difficult for me to communicate to you when to eat the banana. I think many color names are derived in such a way from the attributes of things that are important to people. Of course there are also lots of silly color names that are given by people just trying to sell products and make them sound more interesting. Most of those names have no logical meaning.

Q: How does your eye choose what color to see? Why do certain colors seem more vibrant and some seem more dull?
A: Our eyes are only one part of the process that creates color. We need the stimulus (usually a combination of a light source and an object) together with the human visual system in order to create colors. The color we see (dull or vibrant) depends on the physical properties of the lighting (what wavelengths of light are there and how much) and the object (which wavelengths does it reflect and absorb) and the response of our visual system (which depends on the phsyical stimulus and other variables like the viewing conditions, e.g. color of surrounding area, adaptation, psychological interpretation, etc.). It's putting all those pieces together that makes color science very challenging (and interesting).

Q: How is one tested for color blindness?
Q: How do color blind tests determine if someone is color blind?
A: When someone is color blind, that usually means they have a poor ability to discriminate between certain combinations of colors. The test use various techniques (like numbers on colored backgrounds) to show people these different color combinations in order to figure out which they can and cannot see. Depending on the results, an ophthalmologist (or other tester) can determine which type of color blindness a person has (if any).

Q: After attending a photography program at your college earlier this year, one of the teachers had said that the human eyes can see the color green the easiest. Why is that?
A: Honestly, I would say that you were misled slightly. Our visual system is most sensitive to green wavelengths of light, so if it were completely dark and someone flashed a very dim light in front of you it would be easiest to detect (i.e., the least energy required) if it were a green wavelength. However, at that level of illumination you really couldn't even tell it was colored. This fact about the visual system does not translate into green colors being the easiest to see. There are just too many variables to say in general which color is easiest to see. It would also depend on the task you are trying to accomplish.

Q: Do you attribute the incredibly complex workings of the human eye to evolution or creation?
A: That's a great question. I attribute the form and function of our visual system to evolution. There is clear scientific evidence that evolution does occur. However we certainly don't know everything about evolution and it is more complicated than Darwin originally suggested (as he well knew!). Some, who believe in a single god or all-powerful being, are able to come to terms with both evolution and creation by believing that their god set evolution in motion as part of creation. That is a reasonable religious interpretation, but like all statements of faith cannot be falsified (which is a requirement for science).

Q: Why is it that when you focus on a point between two colors for about 45 sec then look at a white piece of parchment you still see the colors?
A: You don't still see the same colors, but you see what's called a negative afterimage. For example if you stare at a red patch for a while and then look at the white paper, you will see a greenish afterimage. This is due to adaptation in your visual system. Basically, your eyes get tired of seeing a certain color and when you look away this tiredness results in the perception of an opposite color (if your red receptors are tired when you look at white, they will not respond as much as normal and you'll see a greenish color). All of our perceptual systems adapt. For example, if you are outside on a cold winter day and come into a house that is 65 deg., it will feel nice warm. But if you were out on a very hot summer day and went into a 65 deg. house, it would feel very cool. That's adaptation as well.

Q: What causes color blindness?
Q: Why are people color blind and why is it to certain colors?
A: The cause of color blindness is normally that one of the three types of color receptors in our eyes is missing. This is usually an inherited (genetic) trait. Interestingly it is also sex-linked so that females are a carriers and males get the trait (about 8% of males have some form of color deficiency while fewer than 1% of females do!). The deficiencies are to certain colors because of the way our visual system encodes colors. For example, our visual system makes red/green comparisons. If we don't have the red-sensitive receptor, then those comparisons cannot be made and we would be red-green color blind but still able to distinguish other colors.

Q: How do mood rings work when they change color with your mood?
A: They are liquid crystals that change color with temperature. Since our emotions tend to correlate with skin temperature, they do give some indication of mood (although it is not perfect). This phenomenon is called thermochromism (changing color with temperature) and lots of objects do it. You can read more about mood rings at this website.

Q: If we could see other colors in the spectrum (the black area) what would it do to the colors we can already see?
A: Maybe nothing. If our visual systems still responded in the same way to the currently visible wavelengths then we would just have some sort of additional color perceptions (interesting to ponder what they might be). If instead our visual system's current receptors were spread over a larger wavelength range, we would still perceive the same sorts of colors but objects would appear different than we are accustomed to. In other words, the same color perceptions would be reassigned to different objects.

Q: How does a blacklight, which when you look at it the light looks blue and purple, make white objects look brighter?
A: A black light is mostly emitting ultraviolet energy. It looks a little bluish because there is a small amount of visible light emitted as well. White objects look brighter under a black light because most white objects (and the detergent we wash our clothes with) contain fluorescent whitening agents. These agents help to keep white things looking white longer by combating the yellowness that usually occurs when something white gets old or dirty. What these fluorescent whitening agents do is absorb the ultraviolet light and re-emit it as blue light that we can clearly see. This counteracts the yellowing of the white objects and makes them look brighter all the time (not just under a black light. Other materials absorb the ultraviolet and re-emit that energy as other colors (like Day-Glo orange paint for example). The process that causes all this is called fluorescence.

Q: Why are red, blue, and green considered the primary colors?
A: They are not the only primary colors. To a scientist, primary colors are sets of three colors where no one member of the set can be created by mixture of the other two. For additive systems (like a color TV) red, green, and blue fulfill this requirement. They are commonly used as primaries because they allow you to make the widest range of colors in an additive system and therefore the best TVs. Other sets could be selected, but they just wouldn't be as efficient.

Q: What are colors made of?
A: Color doesn't exist without a human observer. So it is not just how the colored objects are made, but how they are illuminated and how we perceive them that matters. It is all these aspects together that create colors. Without the observers there is no color at all!

Q: Why do we have colors?
A: That's a great question. Most of the information in the world can be perceived in black and white (think about how a black and white photograph looks, objects seldom disappear). But we wouldn't have evolved with color vision if their wasn't some advantage beyond simply the pleasure of seeing the world in color. The most accepted theories are that color vision (and therefore colors) exists to help in the location and identification of food (particularly the good food) and in finding mates. There are many species of animals with limited, or no, color vision and they seem to survive just fine, so it is really hard to say for sure. We make colored objects (like our clothes, cars, paint, etc) just because we enjoy them.

Q: Why can we see yellow better than other colors on a black background?
A: The answer has to do with perceived contrast. It is easier to see color combinations that have the most contrast and this contrast is best described as the difference between light and dark. Different colors are more typically found in lighter or darker shades. For example, blues and purples tend to be dark and do show up so well against black (also dark) while colors like yellow tend to be light and show up very well against black.

Q: Why do people see colors differently? (Like how some people will see a color as yellow while others will say its green.)
A: There are physiological differences in people's eyes (both in the lens and on the retina where the light receptors are) that cause small differences in color perception (or large differences if one is color blind). There are also differences in the ways that different people assign names to colors. So a greenish-yellow that you would call yellow might look the same to me, but I would think it is more of a green and use that name instead. In general, however, our agreement on basic color names is quite good.

Q: What does green mean?
A: Colors, or even just the color names, mean different things in different contexts. For example, we think of red as meaning stop, because it has so often been used for stop signs and stop lights. So it is really impossible to give a single answer for any given color. Some interesting thoughts are on this webpage. Maybe that will help.

Q: Why does a blue M&M las longer than any other?
A: I didn't know the blue ones lasted longer, but it sounds like a fun experiment. It is entirely possible that the colorants used to make the blue color interact with that hard candy shell to change it's chemical properties slightly and therefore make the blue ones last longer. Only the M&Ms folks would know for sure. So it wouldn't really be due to the color "blue" but rather the chemical nature of the materials they are using to produce "blue" in the M&Ms.
Followup: If you drop M&Ms in water, the blue ones do indeed lose their color first!

Q: Why do people see color?
A: Most theories about the evolution of color vision suggest two main possibilities. One being that color vision aids in the finding and identification of good food to eat and the second that it aids in identifying healthy mates. Both suggest a selective advantage to color vision that would encourage it's continual passing down to future generations. Other animals seem to do just fine with simpler color vision systems, but there are also examples of animals (including certain insects and birds) that have more complex color vision systems that seem to serve specific capabilities (such as finding the food they are most interested in).

Q: Why and how does a rainbow form? And also what makes the colors in a rainbow?
A: Briefly, rainbows are produced because the different colors of light that make up sunlight are each reflected by raindrops at different angles ... blue goes in one direction, red in slightly different direction, and so on for the colors in between. There is a pretty good explanation of rainbows at HowStuffWorks.

Q: Why do colors affect people's moods? What is it that makes minds react differently to different colors?
A: Colors and moods are of great interest and also the subject of a lot of misunderstanding. It seems that colors do not affect moods in any consistent and intrinsic way. Instead we learn associations and those associations can have huge effects on our emotions and moods. For example, we might learn to associate red with danger and then later on viewing a red color in any context might evoke those feelings of fear, excitement, or anxiety associated with danger. Some of these associations are learned through our society and some are learned through individual experiences. The main thing to remember is that color can have a large affect on our emotions, but it is not the same for every person and the same colors don't affect different people in the same way. There is still much about this topic that is not understood, but it is never as simple as those who like to associate a single color with a single emotion would make you think.

Q: Why can't humans see ultraviolet or infrared energy?
A: There are a few reasons for the range of wavelengths that we can see. One is that much of the interesting interactions between energy and objects happen in those wavelengths, so there is a lot of information for us to see there. There are also more "practical" reasons. UV energy is often damaging to biological tissue, so it would be potentially dangerous for our visual systems to absorb that energy. Some insect respond to UV energy, but they don't live nearly as long as us, so maybe the potential damage is not so much an issue for them. At the other end of the spectrum it becomes difficult for biological photoreceptors to respond reliably. Basically, because of the temperature of our bodies, receptors that could respond to IR would also be very noisy (IR cameras are often cooled for this reason) and it would be difficult for us to differentiate noise produced by our visual system from objects out there in the world.

Q: Why are people with colorblindness unable to see at least one of the primary colors?
A: Actually, people with color vision deficiencies can see all the colors, including primaries. However, the perceptions they have are quite different from those with normal color vision. What happens is that they confuse certain ranges of colors. For example, the most common types of color vision deficiencies result in confusion between reds and greens. They can still see objects with those colors, it's just that they don't look different to them. Here is an interesting website on colorblindness.

Q: Why do colors fade in the evening?
A: There are two things that happen in the evening that make our perceptions of colors fade away. Both are properties of our visual system, not of the light or objects (you can still make nice color photographs at night if you have a camera with enough sensitivity). The first thing that happens is that the color receptors in our eyes are not sensitive enough to light to keep responding as it gets dark. As their responses get smaller and smaller, so do the differences in the color signals from the different receptors and objects end up looking less colorful. As this continues (the light level keeps dropping) the color receptors (called cones) can no longer respond at all. A different type of receptor (called rods) can respond at these low light levels, but the rods do not have the capability to distinguish colors and we basically see in black and white at night.

Q: What color are gamma rays?
A: Gamma rays cannot be directly percieved by the human visual system and thus have no color. While they are electromagnetic energy, like light, they cannot be considered light since that term is reserved for energy visible to humans.

Q: What was the first color invented?
A: The use of pigments and other colorants (of natural origin) dates back as far as our recorded history. I have a nice image of Egyptian paints (still very colorful) from about 1400 BCE!!! As far as man-made, industrially-produced colorants, William Henry Perkin is credited with the first, mauveine, in 1856. It is a purplish colorant. See this website for more information on Perkin. There is a very nice book on the subject of the history of colorants called "Bright Earth: Art and the invention of color" by Philip Ball if you are interested in learning lots of details.

Q: Do different people see color differently?
Q: Do all human beings see colour the same way? E.g. could I see green the way another sees red etc.?
A: We can't really say for sure, but we do know enough about the anatomy, physiology, and psychology of vision to be quite certain that we are seeing things the same way. However, this ultimately becomes a question of philosophy ... do you believe that the experience I have when viewing red is the same as the experience you have when viewing red??? There is no way to prove it one way or the other. That said, there are small physiological differences between people that cause slight differences in color perception. These are particularly noticeable when making critical color matches.

Q: Why is color important in building design?
A: There are two main reasons. One is aesthetics ... just so that the building looks nice and people are happy to work and live in it. The second is more functional. The color of walls, furniture, window treatments, etc. has a significant impact on lighting requirements. If everything were dark colors then it would require much more light for us to do our normal tasks. Lighter colors reflect light around the room more and therefore require less energy consumption to produce the same amount of usable light. This can have an impact on heating costs as well.

Q: How are colors produced in a prism?
Q: Since light travels in straight lines, why do the different colors/wavelengths get separated by a prism?
A: Light travels in straight lines until it hits something. Then it's direction might get changed and it will be off again in a straight line. What happens in a prism is that the light gets redirected (heads off in a different direction) and the amount of that redirection depends on the wavelength. Blue wavelengths are bent more by the prism and red wavelengths less. That means when white light enters the prism it gets separated (dispersed) into a spectrum. The same thing happens in rain drops to form a rainbow.

Q: Why do flowers have bright colors?
A: Flowers are brightly colored to attract attention. They need to be pollinated to reproduce and survive and their colors attract the insects to do the pollination. Insects visit the flowers for food and just happen to help them out by carrying pollen from plant to plant. There is a little bit more at this website.
Also, the bright colors make us like flowers and since we often take care of them and help propagate them, you could say those bright colors help them survive.

Q: Why is it that when we add blue to white clothes when washing, they become brighter?
A: When white cloth ages it gets yellow and looks dull and dingy. Detergents include fluorescent whitening agents to counteract this effect. These agents are blue as you mentioned and they are also fluorescent (they absorb ultraviolet energy and re-emit it as blue light). This emitted blue light makes up for the blue light that would be absorbed by the material as it gets yellower. So, aging takes away blue light and the detergent adds it back in to keep the clothes looking white and bright.

Q: Why can't we see at first when we enter a dark theater?
A: Adaptation. Our visual system adjusts its sensitivity much like an exposure adjustment on a camera. It takes us a little while to adapt to the reduced light levels before our visual system sees well again.

Q: Why do people see better on the sides of our eyes?
A: We don't ... if you are asking about color or detail. We do however, see motion and flicker better in the periphery. It is thought that helps us to notice changes and then look at them. The receptors in those parts of the eye have quicker responses.

Q: Why do people see better on the sides of our eyes in the dark?
A: Our visual system has two types of receptors in the eye. They are cones that respond to color and detail, but require more light, and rods, that are very sensitive to light (we use them when it is dark) and don't respond to color. In the central part of our visual field (where we are looking) there are only cone receptors. That's what allows us to see good color and detail there. However, at night, since there are no rods there, we can't see so well and we have to look just off to the side and use the parts of our eye that have lots of rod receptors but not so many cones.

Q: Why do people sometimes move their heads when they thread a needle?
A: To get better depth perception. Looking at something from multiple angles let's us judge where it is better. And moving our heads lets us keep the hands still (they are doing the threading).

Q: Why do cats eyes shine in the dark?
A: They have a reflective layer in the back of their eye that allows them a second chance to absorb the light and therefore see better in the dark. The tradeoff is that they can't see fine detail as well as we can.

Q: How is a crab eye different from a human eye?
A: Good question. I don't know much about crabs, but here is a site with some information.

Q: How do colors affect people and how do different cultures interpret the meaning of colors?
A: This is a very difficult question. Briefly, different colors affect different people differently. There are definitely emotional affects due to color, but their are no consistent rules. Often such effects are due to learning in a cultural environment and that gets to the second part of your question. Unfortunately that cannot be answered easily either, other than to say it varies from culture to culture. There are a lot of books out there own the topic. You might start by looking at Faber Birren's "Color and Human Response" for a well written and carefully researched introduction.

Q: What do the colors of the rainbow mean?
Q: What do the colors of the rainbow mean, and is there a referance to the meaning in the bible?
A:This seems to be a very popular question. There is no scientific meaning to particular colors, but many people and cultures assign meaning to colors. It's really up to you ... whatever you think they mean! Colors are referenced often in the bible, but I'm not sure the colors of the rainbow were assigned any particular meaning.

Q: Why is silver shiny?
Q: What colors can I mix together to get silver?
A: Silver cannot be simply mixed from other colors. That is because our perception of silver depends not only on the color (which is a gray), but also on the geometrical distribution of the reflected light. It is the way that metals reflect light, not just their colors, that makes them look like metal.

Q: How do different colors affect opaque and transparent objects?
A: Color and opacity/transparency are usually two separate properties of objects, but they do interact. For example, you can have a white opaque object, but not a white transparent object since white happens when most the light is scattered. If a window were white, you couldn't see through it and it would therefore not be transparent. It might be translucent, however, meaning that some light goes through, but is scattered (you see the light coming through, but you can't see objects clearly on the other side).

Q: What colors travel faster than others in the spectrum?
A: In a vacuum, all colors of light travel at the same speed. The same is essentially true for air. However, in some materials the speed of light depends on wavelength and that is what causes dispersion (the separation of colors by a prism).

Q: Why do colors have numbers, and what does each color repersent?
A: Colors have numbers to facilitate communication. Our assignments of numbers help people communicate more precisely (and accurately) about color than they could with names alone. Colors, by themselves, don't represent anything. Sometimes they are put in a context that gives them some meaning, however (like signal lights).

Q: Why do colors fade?
Q: What color fades fastest in sunlight?
A: Colors fade because of chemical reactions that break down the colorants in the object. Colorants are the various chemical compounds that interact with light to produce colored perceptions. The causes of the breakdown of colorants can be from exposure to light, to heat, to other chemicals (such as air), etc. It is very hard to say which colors will fade faster because it depends on the specific colorants, the object, and the environment it is exposed to.

Q: What does it mean when the moon is an orangy color?
A: It doesn't mean anything. What causes it is that the moon is low in the sky, near the horizon and you are viewing it through a larger thickness of our atmosphere. The cause is exactly the same as the cause of a reddish sunset. More atmosphere between you and the moon scatters more blue light away (which is why the sky is blue), leaving only the reddish light from the moon to reach your eye.

Q: Is it true that colour exist only in our eyes and brain but actually in the universe everything is without color because it is energy and energy has no color?
A: Yes, color is a perception. Without an observer there is no color. The physical stimulus of color (light and its interactions with objects) might be present, but without an observer that is just energy. It is our perception of that stimulus that is color.

Q: What are the primary colors?
Q: What creates the primary colors? Why do people say they are red, yellow and blue?
Q: What is the definition of primary colors?
A: The primary colors are just like any others. What makes them "primary" is a somewhat arbitrary definition of a color mixing system. For example, in color television red, green, and blue are primaries while in color printing cyan, magenta, and yellow are primaries. For a scientist, the definition of a set of primaries is that they are three colors with the property that none of them can be produced from a mixture of the two. The number three comes from having three cone responses in our visual system.

Q: What is the definition of secondary colors?
A: Secondary colors are usually defined as mixtures of two primary colors in whatever primary system you might be working with.

Q: why do some fish change color by the change in their mood? Is this in any way related to "color-emotion"?
A: Hmmm ... how do you know the mood of a fish?!!! Actually there are some people that claim fish are incapable of moods, feeling pain, etc. Those are people that like to catch fish and hurt them. I happen to disagree. OK, so on to the actual question. From what I understand, the changing colors of fish are similar to the changing colors in other animals like chameleons. Various stimuli cause the color changes, but usually they happen for some fairly obvious reason like to hide from predators, scare them away, fool them, or attract a mate (or food). I don't think it is so much mood as the surroundings that cause the change. (However, I am not a fish expert, so I could be wrong!). As far as colors and emotions ... color is a very personal experience and can evoke strong emotional responses. However, these are personal and not necessarily the same response (or same strength of response) for each person. There are no consistent emotion-color relations that apply to everyone.

Q: Do we all experience the same thing when we observe a color, or have we just all learned the same names to associate with certain perceptions?
A: All our scientific understanding about color and perception suggests that we have similar experiences. However, we can never be 100% certain since it is impossible for one person to say what is truly being experienced by another and we are taught the names for colors. This really ends up being a philosophical question that we can all ponder and discuss for fun.

Q: Which colors catch your eye the fastest?
Q: What is the for the human eye to see? For example in searching for plane wreckage.
A: Our visual system functions on "contrast", so the easiest color to see is the one that contrasts most with the background. So I really can't give you a single answer. As far as the plane wreckage, the same would hold true ... whatever color contrasts most with the surroundings of the wreckage. I'm not sure you can predict that in advance.

Q: What do I tell the paint store to mix in order to get a color that best matches a wavelength (5040 Angstroms)?
A: You really can't make paint that is a perfect match to light of a single wavelength. In this case, the wavelength selected (5040 Angstroms or 504 nm) would appear cyan, or bluish-green, if viewed in isolation. Since paint doesn't reflect just a single wavelength, you can't reproduce this physical stimulus with paint. Even if you could, it would be very dark since it would be absorbing most of the visible spectrum. The best you can do is make a visual approximation. For this wavelength, you could go to the paint store and select the paint sample that is bluish-green (about half way between an ideal green and ideal blue) and as bright and chromatic (saturated) as possible.

Q: How does color-changing Silly Putty work?
A: It is based on thermochromism, the tendency for materials to change color with changes in temperature. Some materials exhibit large thermochromic shifts. According to the Silly Science site ...
Here's the scientific skinny on color-changing Silly Putty: "Silly Putty uses thermochromic (a big word for color change through temperature change) to change color. Changeable Silly Putty is formulated with a base color, to which an additional thermochromic dye is added. When the putty is handled, body heat causes a chemical reaction that makes the thermochromic dye disappear, leaving only the base color. (For example, purple to pink change happens when the base color is pink and the thermochromic dye is blue. Take blue from purple and you get pink.) When the putty cools, the dye "recongeals," returning the color.

Q: Why are school busses yellow and how are they all made the same color yellow?
A: School busses are yellow to make them very noticeable and they are a consistent yellow to help with this recognition. School Bus yellow is a standardized color with specific tolerances and numerical definitions. Techniques of color measurement, along with visual assessment, are used, to assure that each batch of school-bus yellow paint, and each painted bus, fall within the standard specifications. Yes, even the color of your school bus relies on science.

Q: Why can't I see colors at night?
A: Because the light receptors in your eye responsible for color vision, the cones, require more light to function. They just aren't sensitive enough to respond and therefore cannot produce the signals required for the perception of color. You have a second type of receptors, called rods, that allow you to see at night with very little illumination. However, rods are not capable of producing color vision since they all have the same response to different wavelengths of light.

Q: Why is the sky blue?
A: It is blue due to scattering of light in the atmosphere. The particles in the atmosphere interact with light in such a way that they scatter more blue light than other wavelengths. Thus red and yellow light tends to go straight through the atmosphere (why a sunset appears red when you look at it) and blue light is scattered so that the rest of the sky looks blue. When there are clouds, the water droplets and ice crystals in the sky are large enough to scatter all wavelengths equally. Thus the clouds appear white or gray.

Q: Why do I sometimes see fuzzy colors when I close my eyes after viewing a bright light?
A: You are seeing afterimages. Afterimages happen when your retinas (the light sensitive parts of your eyes) are exposed to strong lights. Basically the retinas become less sensitive to light when exposed to a lot of it and when you close your eyes you are seeing the different response of different parts of your retina to the absence of light. Colored afterimages are sometimes used to create visual illusions.

Q: Why are eyes different color?
A: I'm not sure there is a good reason for the eyes to be colored at all. However, our eye color is produced by a pigment called melanin, the same pigment that colors our hair and skin. Different colors are produced by different amounts and distributions of the melanin. For example, blue eyes are produced by relatively small concentrations of melanin distributed through the iris (the colored part of our eyes that forms the pupils) in small clumps. This produces more scattering of blue light than other colors and makes for blue eyes in a manner similar to how the blue sky is produced.

Q: Does eye color have any affect on visual perception?
A: None that has been well documented. In visual experiements on color perception, we never worry about the eye color of the observer.

Q: Why is a rainbow?
Q: How does a rainbow form?
A: Because we enjoy looking at them. As far as a simple explanation of how they occur, I just like to say the different colors of light are bent to different angles by the raindrops in the air. Howstuffworks has a nice explanation of rainbows. Other good sources of information are the "Magic Schoolbus" books on color and the senses.

Q: How many colors in the rainbow?
Q: What are the colors of the rainbow?
A: Lots! We see a continuous range of hues in the spectrum due to the amazing color sensitivity of our visual system. A rainbow is this spectrum spread across part of the sky, so there is also a wide range of hues perceptible in a rainbow. The number of hues we can discriminate depends on the viewing conditions. In ideal viewing conditions, it is probably around 100 or so. In less ideal conditions, the number might fall to 10 or fewer. The important conditions include the brightness of the rainbow, its background, and its size and shape. (While most natural rainbows will be of the same angular size, their perceived size can vary and man-made rainbows can be of all sorts of sizes and shapes.)

Q: Why does the rainbow have so many colors?
A: See the previous answer for some insight. In addition, it is due to the way oru visual system responds to different wavelengths. The sensitivities of our cone receptors are such that it is possible to compare their relative responses throughout the visible spectrum. It is these comparisons (or ratios of responses) that produce the wide range of hues we perceive. If each cone type responded to distinct regions in the spectrum, then we would only be able to percieve three hues in a rainbow ... some cameras work this way and produce disappointing images of a spectrum.

Q: Why can't two people see the same rainbow?
A: The apparent location of a rainbow depends on the geometrical relationship between the light source (usually the sun) and your eyes. Since no two people can put their eyes in exactly the same position at the same time, they must be viewing rainbows in two slightly different positions.

Q: After it rains, how long does it take for a rainbow to form?
A: Rainbows form while it is raining and the sun is out. There is no time delay. Essentially, there should be sunshine where you are and rain in the direction you face when you look away from the sun. Rainbows are always in the same location relative to the sun and your eyes.

Q: How do glow sticks work?
A: Chemiluminescence. In this process a chemical reaction (started when you mix the two chemicals in the stick) provides energy to a luminescent material that takes that energy and converts it into emitted light. As long as the chemical reaction continues to provide energy, the glow stick will continue to produce light. Details, details, details.

Q: Why do glow sticks last longer when they are put in a freezer?
A: Since the energy used to create the light comes from a chemical reaction, the longer you can make that reaction keep running, the longer the glow stick will produce light. The rate of chemical reactions depends on many things such as the avaialability of the reactants (have the necessary chemicals been used up?) and the application of outside energy (more energy generally speeds up the reaction). When you put the glow stick in the freezer, you are removing a source of outside energy (heat from the environment) and this will slow down the reaction and thus allow the stick to produce light for a longer period. An unfortunate side effect is that the cold glow stick will also produce less light.

Q: Does color aid in the comprehension of information?
A: Absolutely! But it can also get in the way if not used appropriately. Think about a stop light. All the information about whether you should stop, go, or slow down is available from the location of the three lights (top, middle, bottom), but it would be much more difficult to comprehend that information if all three lights were the same color. Having them three distinct colors (red, green, yellow) makes the information much more readily accessible. I'm sure it is easy to think of many more examples like this one.

Q: What is brown?
A: Brown is dark, low-chroma (desaturated), orange. In other words, an orange light that is perceived in an environment that makes it look dark and less saturated will appear brown. A brighter surround is such an environment. Brown is a special sort of color perception that requires this relationship to its environment in order to be perceived. That's why you can't go to a hardware store and buy a brown light bulb!

Q: Do animals (my pets) see color?
A: Unless your pet is one of a very few species of monkey, they don't perceive color in the same way we do. Interestingly, some fish, such as goldfish, also have color vision systems fairly similar to our own (maybe even better!). Many birds and insects also have highly-developed color vision systems, although quite different from ours. However, most animals are essentially "color blind". Most are considered dichromatic, meaning they have two types of cones and see a limited range of colors. This is similar to what we call "color blindness" in humans. Normal human vision is trichromatic, meaning there are three cone types and our color perceptions require three attributes to describe (lightness, saturation, and hue). Those goldfish, and some others, are tetrachromatic, meaning there are four types of color receptors.

Q: Why can some animals see certain colors but can't see others?
A: Some animals respond to entirely different wavelengths of energy than we do. For example, bees and other insects can see ultraviolet energy. Others don't have the same type of color vision system that we do and are not able to distinguish the same range of colors that we can.

Q: What is the most important number in color?
Q: What is the importance of the number 3 in color?
A: Three. Because we have three types of color receptors in our eyes and that results in the three-dimensional nature of color matching, color mixing, and color appearance.

Q: What is high-dynamic-range imaging?
A: Most images encode the range of light in a scene using 256 levels (or numbers, 8-bits). A high-dynamic-range (HDR) image includes a much greater range of information about the the light in the scene (sometimes essentially all of it) and is encoded using 13 or more bits of information (8192 or more levels) per color channel. Such images allow the recording of more scene information than we can usually percieve and therefore are useful in studing human perception. See my HDR Photographic Survey for more information and examples.

Q: How do digital cameras work?
Q: How do digital cameras record color?
A: Digital cameras are designed to somewhat mimic our visual system. They have sensors that respond to three regions of the spectrum, red, green, and blue. The responses of these sensors are then encoded as numbers that are used to drive displays or printers in order to reproduce the colors origincally detected in the scene (at least approximately). Of course there are many more details to the the process.

Q: How do color printers work?
Q: How does a color printer make color?
Q: How do computer printers work?
A: Howstuffworks has an article on ink-jet printers and links to more information. In a nutshell we have only three types of color receptors in our eyes and the primary colors in a printer work to control the responses of those three receptor types. Since there are only three receptors types, only three primaries are required. Most printers use combinations of cyan, magenta, yellow, and black ink to produce color. Cyan controls the amount of red light, magental the green light, and yellow the blue light reflected from various parts of the print. Black is used for text and as a cheaper alternative to equal amounts of cyan, magenta, and yellow ink in appropriate areas of the printed image.

Q: What does the world look like to color blind people?
A: It is impossible to say exactly, but we can figure out which colors they cannot distinguish and produce images that represent a "best guess". vischeck.com provides a website that explains color blindness in detail and has software that allows you to create images to illustrate the different perceptions of people with different forms of color vision deficiencies.

Q: Do girls really see color better than boys?
A: No! However, due to the genetics of color blindness boys are far more likely to have color vision deficiencies. However, if a boy and a girl both have normal color vision, then there certainly will be individual differences, but they are not correlated with gender. Boys and girls with normal color vision have the same visual performance. It is possible for some girls to have four types of color receptors (cones) instead of the normal three, but this appears to have little, or no advantage in color discrimination in everyday life, and can only be determined genetically (or with extremely specialized visual experiments), not perceptually. So the general answer is "no".

Q: How does additive color mixing work?
A: Additive mixing happens when two or more light sources are superimposed by either illuminating the same spot or by being so close together in space and time that oure visual systems cannot distinguish them. What we perceive is the sum of the energy from each of the lights. This is how computer displays and televisions reproduce color. Red, green, and blue are common additive primaries since it is easy and efficient to makea wide variety of colors with them.

Q: How does subtractive color mixing work?
A: Subtractive mixing happens when two or more dyes or pigments are combined by either layering or mixing them. Each dye or pigment absorbs certain colors (wavelengths) and what we perceive is the light that remains after each colorant has absorbed its part. This is how some printing systems and paint mixtures produce various colors. Cyan, magenta, and yellow are common subtractive primaries since it is easy and efficient to makea wide variety of colors with them.

Q: Why do objects appear about the same color regardless of changes in illumination?
A: Often we are most interest in the material properties of objects (e.g., is the banana ripe) so our visual systems "discount" the effects of varying color and amount of illumination. This happens through various processes of chromatic adaptation. This process is not perfect as it is useful for us to also perceive information about the illumination itself; otherwise it would never get dark at night!

Q: Is there a connection between color and emotion?
Q: How does color affect our mood?
A: Absolutely! There is no doubt that color can have as large impact on our emotions and moods. However the effects (both the type and strength) are very individual. A color that makes me feel happy or energized might make you feel sad or tired. There are various reasons for these responses, but essentially they are learned from either cultural practices or significant individual events. There is a lot of misinformation on this topic. A good book for more information is Faber Birren's "Color and Human Response".

Q: What do all the colors mean?
Q: What does each individual color mean?
Q: M&M Colors mean?
A: Like the emotional effects of colors, the meaning of colors is an individual response. Colors can be assigned certain meanings by an individual or culture, but they have no instrinsic meaning on their own. Birren's book "Color and Human Response" also addresses color meaning. M&Ms are a great example. There are certainly stories out there around the schoolyard of various "meanings" or "effects" of the different color M&Ms. To the extent they are real is simply a matter of psychology. If you believe there is a certain meaning to green M&Ms, then there is. If you choose not to believe, then there isn't. Right now I am looking at a map of the USA and the various states are colored red, orange, yellow, green, and blue. My home state of NY is colored orange. On that map, there is no particular meaning to orange (Wyoming is also orange) other than to indicate that a state is different from its immediate neighbors. Other maps might assign particular meanings to the colors (e.g. coding by population density, or rainfall, or whatever).

Q: Do SAD lights work?
A: Yes they do. SAD is short for seasonal affective disorder in which people become more depressed in the winter months when there is significantly less daylight. Scientific research has clearly shown that relatively brief exposure to high-intensity light (e.g., an hour reading next to a bright lamp) can lesson the effects and make people feel much better through the winter months. The positive effects apparently depend on light intensity and not color and the exposure doesn't have to be through the eyes. Remember that our skin responds to light as well ... some exposure to sunlight is good for us; too much can be very bad.

Q: When someone takes a picture of you, why do you get red eye?
Q: When someone takes a picture, how does a person get red eye?
A: What you are seeing is the reflected light from the blood vessels and other structures in the back of the person's eye. Since our eyes, like a camera, focus an image of the world on the back of the eye (the retina), red eye happens when the subject looks at a camera with a flash near the lens (like a small point-and-shoot camera) when the picture is taken. Since the subject is focusing on the camera, that means that the flash is focussed on the back of their eye (why it looks so bright!) and the back of their eye is focused on the camera. What you end up with is the whole pupil filled with that image of the back of the eye (red). Red eye can be reduced if there are lots of lights on so that the subject's pupil is smaller, by looking away from the camera, or by moving the flash farther away from the camera lens.

Q: Why do people get red-eye in photographs, but animal eyes glow green?
A: Our eyes have a dark layer behind the retina that absorbs any light that our receptors (rods and cones) miss, so the reflected light in the photograph is mainly from blood vessels (red). Nocturnal animals have a different structure. Their eyes have a reflective layer behind the retina that passes the light back through the receptors giving thema second chance to detect the light. This makes these animals much more sensitive to light. When they are photographed, instead of the red eye you see with people, you see this strong reflection that is often yellowish or greenish. This is also why you see animals eyes glowing at night when car headlights fall on them. Since they are looking at the lights, people near the lights see a bright reflection of their eyes. Another way to say it is that their eyes act like retroreflectors returning the light toward its source (road signs also do this).

Q: How does a computer represent colors as numbers?
A: There are many ways that computers represent colors as numbers. Any numerical specification of a color can be represented as binary digits in a computer. The most common representation in computers is as RGB values expressed in the range from 0-255. That is using 8-bits of binary information to represent amounts of each of the red, green, and blue primaries on a given computer display. The actual color you get from a given set of RGB values will depend on the display used and the software interpretation of the numbers. Basically, zero means to not display any red, green, or blue and 255 means to turn the display fully on. Thus a white color can be represented by R = G = B = 255 and black by R = G = B = 0. A full display red would be R = 255, G = 0, and B = 0. Etc.

Q: How are colors measured?
A: Thre things must be quantified to measure color, the light source, the object (if there is one), and the human observer. Color is measured by determining the amount of energy at each wavelength in the visible spectrum for the light source and the percentage of that light that is reflected by the object. The human observer is then characterized through average responses of the cone receptors in the eye to allow computation of the color response produced by the measured stimulus (light source and object combination).

Q: Why arenít my photographs the same colors as the original scenes?
A: There are many reasons. One big one is that people often prefer the colors to be different (brighter and more saturated) since our memories of colors are often more vivid than the reality of the original scene. Beyond that there are limitations in the camera and printer that make it very difficult to reproduce colors accurately. The color responses of the camera are different than those in our eyes and the color combinations of the inks or dyes on the paper cannot exactly reconstruct some colors. Lastly, we often view the photograph in different conditions (light level, light color, size of image, etc.) than the original which has an affect on our perceptions.

Q: Why does snow look brighter than the sky?
A: This is a puzzle. On a cloudy day, all the light is coming from those clouds, but yet the snow looks brighter. This is due to both some optical and perceptual effects. Optically, the geometry of illumination and viewing produces the effect since every location of the snow is illuminated by the full sky while each part of the sky only has light from itself. Perceptually, we tend to discount the illumnination (clouds) and view the snow as an object in contrast to other objects in the scene ... and the snow is the brightest object.

Q: How do you make a color like copper or gold on a monitor or printer?
A: It turns out that if you look only at diffusely reflected light, gold is yellow, silver is gray, and copper is brown. That is exactly what you often see on your monitor or printer when you try to make these colors. The appearance of metals depends on their unique characteristic that their first-surface (or specular) reflection (the highlights on an object) are also colored. This is the appearance difference between a yellow piece of plastic (white highlights ... the color of the light source) and a piece of gold (yellow highlights ... the color of the object). The only way to render these appearances on a display is to add some dimensionality. In other words you can render a 3D object on your monitor that looks like a piece of gold, but you can't make a flat patch of color that looks like gold (unless you render different views of it).

Q: How/Why did color vision evolve?
A: Color vision has evolved in parallel in some mammals (like humans), in insects, in birds, and in fish. Thus there has been some selective advantage for each of these different types of creatures to have color vision. For humans, the evolution appears to be that there was first short-wavelength-sensitive cones and then a single type of long-wavelenght sensitive cones. Thus earlier visual systems were red-green color blind and this is still seen in most mammals. Such a visual system is quite effective in discounting the effects of natural illumination. Lastly, the division of long- and middle-wavlength sensitive cones developed to produce trichromatic vision like we have today. It is thought that this last adaptation helps in the identification of ripe food and healthy mates.

Q: Is your vision affected by the color of your eyes?
A: I know ofno relationship between visual performance and eye color. In fact, it is not clear that differences in eye color serve any purpose in everyday life beyond helping us identify people (maybe that is important enough?).

Q: What is the smallest perceptible color difference?
A: That is a difficult question because the answer depends on the system used to quantify, or measure, color. However in optimal viewing conditions it is possible for our visual system to detect changes in the amount of light as small as one-tenth of one percent. This is a very small change in color and helps us to understand the wide range of color perceptions we are capable of experiencing.

Q: What is the meaning of the Munsell and similar color notation systems?
A: The Munsell system can be considered as something like a "dictionary" or "atlas" of colors. In fact the first version was called "Atlas of the Munsell Colors. In Munsell, each object color perception is given three notations, one for lightness (Value), one for hue, and one for chroma (similar to saturation). With those three numbers, one can unambiguously specify a certain object color and communicate it to others. For example, my bright red car has the Munsell notation 4R 3/12. 4R defines the particular red hue (nearly a unique red with just a touch of blue ... sort of blood red). The value of 3 tells us that it is slightly darker than a middle gray (value 5) and the chroma of 12 tells us that it is a very vivid, saturated red. So the meaning is just a quantitiative way to name colors. Other systems do the same thing with different notation methods.

Q: Why do some colors of popsicles melt faster than others?
A: When light is absorbed, that energy is normally converted into heat and thus raises the temperature of the object. Darker colored objects are darker because they absorb more light. Thus, since the darker objects absorb more light, they will warm up faster, and the darker-colored popsicles will melt first.

Q: How do spinning color wheels work?
A: These wheels have segments of different colors. When they are spun very quickly, our eyes cannot respond quickly enough to see the individual segments and we see a single color that is the additive combination of the light reflected from the segments. It is the same additive mixture you would get by projecting lights on top of one another.

Q: Why does light create color?
A: Because color is a visual perception and our eyes respond to light. Since we have three different types of cone receptors in our eyes, that respond, differently to different colors (wavelengths) of light, we are able to compare those three responses and perceive a wide variety of colors. Light is the physical stimulus for our perception of color.

Q: How do fluorescent colors work?
A: Fluorescent objects absorb energy of one wavelength (often ultraviolet or short-wavelength violet or blue light) and then re-emit that energy at longer wavelengths (like orange or green). This happens because a little bit of that absorbed energy is lost to heat and photons (light particles) of longer wavelengths (yellow, orange, red) have less energy than those of shorter wavelengths (ultraviolet, violet, blue).

Q: How do artificial light sources work?
A: It depends on the type of light source. Incandescent light bulbs work by passing electricity through a tungsten filament. This causes the filament to heat up and when it gets hot it emits light (unless it gets too hot and burns up!). Most materials will emit light this way, but often they burn before they get hot enough to emit visible light. Fluorescent lights work in a completely different way. They pass electricity through mercury gas. This gas then converts some of that energy into emitted light at very specific wavelengths. Much of this energy is in the ultraviolet. The lamp is then coated with a phosphor material that absorbs that ultraviolet energy (and maybe some of the visible light) and then emits that energy in the color selected by the lamp designer (that's whay there are many types of fluoreseent sources. Light-emitting diodes, LEDs, work by a simple electronic stimulation of the material which converts that energy directly to emitted light (that's why they are very energy efficient). Howstuffworks.com has nice explanations of many of these phenomena.

Q: Why do colors fade?
A: Objects often get their color from chamicals that we call colorants. Chemical reactions can change the nature of these colorants which, in turn, can change how they interact with light and therefore their color. These reactions are often caused, or enhanced, by exposure to light, heat, moisture, or other chemicals. Thus, all of these factors can contribute to the fading of colors. Some objects, such as gemstones, are very stable and resistant to fading.

Q: How/Why do we adapt to color?
A: Adaptation is an integral part of all our senses. When exposed to any stimulus (light, odor, heat, pain, etc.) our sensory systems become fatigued and therefore less sensitive to that particular stimulus. When we first turn on a light in the morning it is dazzling, but we quickly become less sensitive and everything returns to normal. The same is true when we walk into a darkened room; at first we can't see anything, but gradually our eyes become more sensitive and we can see objects again. The same is true for color, we adapt any colors we are exposed to. There are many mechanisms for visual adaptation such as dilation and contraction of our pupils, changes in sensitivity of our light receptors, and cognitive interpretation of the stimulus. As for "why", in general adapation helps us to ignore things that aren't changing and be more sensitive to changes around us. For example, we aren't too sensitive to the overall color or level of illumination in a scene, but we are quite sensitive to the changes in colors of objects in the scene.

Q: Can a viewed color affect the performance of tasks, like exams?
A: Probably not very much, but there is some recent research that shows an "aversion" response to the color red. If people are exposed to red just before taking an exam they perform slightly less well than if they were exposed to a different color. The cause of this aversion response is not yet known; it could be learned or it could be something intrinsic that causes us to "fear" red (just a little). This has also been found in sporting events where athletes dressed in red tended to be more successful ... perhaps because their opponents were viewing it and having an aversion response (rather than the red having an effect on the athlete wearing it).

Q: What colors can you see best in the dark?
A: Well, you can't see any colors in the dark since there is not enough light for our color system to function. However, certain objects might be easier to see in the dark. Since our rod receptors respond best to wavelengths that would look blue in the daytime, blue objects tend to look lighter than other colors at night. Thus, if looking for objects on a dark background, things that look blue in daylight would be the easiest to see at night.

Q: Does Baker-Miller pink actually work?
A: Yes and no. It can have a measureable effect on people, but the effect also wears off quite quickly. There are also other factors involved in any situation that are likely to have a larger effect. It is interesting to contemplate though. Here's a link with some more information.

Q: Can light be captured inside an opaque container?
A: Theoretically, yes! Unfortunately the container would not only have to be opaque, but a perfect reflector (reflecting 100% of the incident light) on the inside. If the inside was anything less than a perfect reflector, then there would be some probability that light would get absorbed each time it strikes the surface. Since light is traveling so quickly, it wouldn't take long for all the light to get absorbed. Unfortunately there are no such materials to build the container from and, even if there were, you'd have to figure out a way to remove the light source from the container and seal it (so that it was perfectly reflecting on all surfaces) before the light escaped from the opening. That would be quite a challenge indeed. Also, once you opened that theoretical container the light would all escape instantaneously so that the most you might see is a very brief flash.

Q: Why does the spinning Benham top look colored?
A: There is not a simple explanation for the colors observed. Clearly they are based on some mechanisms in the visual system responding at different temporal rates, but the correlation with the patterns and simple assumptions about the rate of cone responses is not easily shown. The color probably depend on differences in higher level visual mechanisms as well. There is a short discussion with links here.

Q: Do we dream in color?
A: Yes. I regularly experience both black-and-white and color dreams. There has been folklore that people only dreamed in black and white, but that appears to be the result of poor dream recall and cultural influences. There are some interesting references on this page on the topic. Some say that all dreams are in color, but we sometimes don't remember the color. Since we experience black and white images both in natural settings (as in low luminance levels where we lose color vision) and through technology (black and white photographs and video), there is no reason to believe we couldn't replicate that perceptual experience in a dream.

Q: Why do we dream in color?
A: Why wouldn't we? What we see in dreams is believed to be stimulation of the visual areas of the brain from the brain itself rather than from our eyes. If those areas of the brain can help us perceive color based on the signals from our eyes, why shouldn't they also be able to produce color perceptions when stimulated by the brain? Besides, colorful dreams are often far more enjoyable than black and white dreams.

Q: What color is the universe?
A: It all depends on how you look at it. If seen in isolation from a large distance outside the universe (ponder that!), it would appear white. If you take the average energy distribution of the universe and look at as a stimulus under average daylight on earth, then it would look like a pale beige. It turns out the average distribution of energy in the universe is not too different from average daylight here on earth. That alone is pretty amazing. Many more details on this topic can be found on this website.

Q: What is the minimum change in wavelength we can perceive?
A: Our ability to perceive changes in wavelength depends on several variables, most important of which are the wavelength itself and the luminance level, or amount of light. As a general rule of thumb, it is reasonable to say that we are able to detect changes in wavelength of about 2nm in the middle of the visible spectrum. At the ends of the spectrum this number increases and it becomes undefined at the very ends of the visible spectrum where only a single type of cone photoreceptor is responding to the stimulus. Some classic measurements of wavelength discrimination show that wavelength discrimination can be as good as about 1nm near 500 and 600nm, around 2nm for much of the visible spectrum and then in excess of 5nm for wavelengths below 430nm and above 650nm.

Q: Why do lobsters turn red when they are cooked?
A: Simply put, the red colorant is the most stable component of the coloring in a lobster shell. The greens and browns that darken the shell in a live lobster are destroyed by cooking. For more details with the actual chemical compunds involved, see this page.

Q: Why do night-vision systems often produce images only in green tones?
A: It probably comes from the first displays that were used with the systems (likely monochrome CRTs with green phosphors). There is no good color science reason for the display to be green. The night vision systems work by collecting infrared images that contain no color information. They must be displayed somehow and any monochromatic display would work (sometimes false colors are added to try to help distinguish areas). It would probably make the most sense to use a red display since it would be easy to see details with our long-wavelength cones and not disrupt the dark adaptation of our rods (useful when lookind directly at the scene).

Q: Is it possible to accurately remember a given color?
A: No. Our ability to remember colors is quite poor. At best we can remember only general categories of color represented by significant color names. That's why there are so many sophisticated ways to name, organize, and measure color.

Q: Is the color of red wine a reliable indicator of its quality?
A: Not at all. It might work within a single very limited type of wine, but would certainly not generalize. I have done very extensive measurements of beer color and the same is true. Good beer and wine come in a wide variety of colors, but unfortunately bad beer and wine can span that same range. That said, color is used to control and examine the brewing and fermenting processes and it is important to make sure the product is consistent as possible because whether they should or not, customers do associate quality with color.

Q: Why does the human visual system have two opponent chromatic channels?
A: We have two since there are two color dimensions left to encode after the luminance (light-dark) information is removed and our three cone types produce a three dimensional response. The organization into light-dark and two chromatic channels allows the visual system to devote the most processing power to the light-dark channel that includes most of the information in the visual world. That's why black and white photographs look so good and objects seldom disappear in black and white images.

Q: Why do colors of stained glass windows look so beautiful and different than colors of other objects?
A: First, the colorants used are often very saturated. Then the viewing conditions are ideal where the windows are viewed in a darkened environment (no flare light to wash out the colors) with very strong illumination behind them. Notice that they don't look colorful at all from the outside in the daytime. At night the roles are reversed and the windows look colorful from outside the building, but not colorful at all from the inside.

Q: Who first described the idea that color is a combination of light, plus object, plus eye?
A: We don't know. We can go back as far as Aristotle and find amazingly accurate insights into color perception (with a lot of misconceptions as well). It is probably safe to say that such descriptions of color date back before our recorded history. Our modern understanding began to form with Isaac Newton (1600s), followed by others such as Helmholtz, Maxwell, Young, and Hering (1800s).

Q: Why is green often used for surgeons scrubs?
A: To help break up the afterimages that they see after looking at red (blood and human tissue) for long periods of time. If they looked away at a white wall, they would see greenish afterimages of the areas they had been working on. Such afterimages are probably quite disturbing during a long procedure.

Q: Is there a best color for sunglasses?
A: Yes, but it depends on what task you are performing. For general purposes, the best color is gray since it will not affect the color appearance of anything, but just make the scene appear a little darker). However, the color of glasses could be used to enhance certain objects (e.g. purple to enhance discrimination of green objects) or to have other effects. For example yellow glasses help improve visual acuity by removing the blue wavelengths that are poorly focused by our eyes and also scattered alot in the atmosphere.

Q: Why does water in the sea show so many different bluish colors?
A: There are several reasons. One is that the water might simply be different in different places. For example there might be varying amounts of sediment or creatures suspended in the water. Another is that the appearance depends on how water is viewed. Things like the angle of the sun, the position of the observer, the background, and the depth of the water will all have an effect on the perceived color. Some very beautiful color perceptions are created when the water is very deep and clear (like Crater Lake in Oregon) or when there is bright sunshine and white sand under the water (like in the Carribean where the pirates used to hang out).

Q: How many color names exist?
A: This question has been of interest not only to scientists who study color and the visual system but also to linguists and philosophers. The conventional wisdom used to be that culture and language determined our use of color names. This view began to change in 1969 when Berlin and Kay published a book that showed that there is a high degree of universality in the use of color terms across cultures and languages. Now many investigators believe that there is a physiological basis for the use of certain basic color terms and the parsing of color space into categorical regions denoted by these basic color terms (black, white, gray, red, green, blue, yellow, purple, orange, brown and pink). There is evidence from animal studies and studies with infants to support this categorical view of color.
However, people do use many more color words; hundreds (if not thousands) of different terms have been catalogued. It seems however that the non-basic terms are used without the same generality and consistency as the basic terms. For example, cyan may have a specific meaning to a couple of printers working together in a print shop but the man on the street may have an altogether different notion of what cyan is. Yet everyone, within the limits of the homogeneity of normal color vision, will agree about the meaning of orange or pink

Q: Why does it get darker outside when I turn on the lights inside?
A: It is an effect of contrast and adaptation. Of course, turning on the lights inside has no effect on the actual amount of light outside. What changes is our perception of that light. Since we quickly adapt to the light inside, and judge the light outside in contrast to it, the additional light inside the house makes whatever light is outside be perceived as less, or darker.

Q: Why can I see well outside in the evening when my mom (who's inside) thinks it's too dark to be out.
A: Because you have been outside as it gradually got darker, you have adapted to the lower and lower levels of illumination and can see just fine.
On the other hand, your mother has been inside, and probably turned on the lights, and she has adapted to that level of illumination. When she glances outside, it looks very dark to her because she hasn't had the time to adapt to the low light level like you have. Many an outdoor play session has been ended early because of these adaptation effects. Mom should come outside and play too!

Q: How can we see different colors like purple and orange when no two colors mix to make them?
A: We see them becuase they produce a given combination of responses in our visual system. And it is easy to make purple or orange out of combinations of two colors.

Q: Why can't we see all of the different colors within one color?
Q: Why can't we see the spectrum?
A: Bucause our eyes do not have the detectors necessary to discriminate all the wavelengths. Instead we have three types of cones roughly sensitive to the red, green, and blue regions of the spectrum and we see various colors by comparing the relative responses of these three types of cones. Our brains simply do not have access to the detailed spectral information. This is another way to describe the phenomenon known as "metamerism".

Q: I know that mixing the different colored lights will create different colors, but how does the light affect how bright a color appears? Is it the more light, the brighter the color? Less light would mean a darker color?
A: When simply mixing colored lights, yes, more light will make brighter colors. However, when illuminating a scene of many colors, more light will result in more perceived contrast. That means that bright colors will look brighter and dark colors will look darker with more light!

Q: Do all of the colors that make up white light travel at the same frequency until they pass through a prism?
A: They all have different frequencies, but travel at the same speed. Frequency and wavelength are directly related to one another. When they pass through a prism, they retain their frequency, but each frequency travels at a different speed. That is what causes the dispersion in a prism that separates the various wavelengths into a spectrum.

Q: Taking art classes, I have learned different complementary colors than I have just learned in physics class. In art blue is the complement to orange, yellow to purple, and red to green. In physics, it is blue to yellow, red to cyan and green to magenta. Why is this?
A: Complementary colors are defined in different ways. In physics it is often the two lights that will add together (additive mixing) to produce white. In art it is often the two paints that will make a neutral color when mixed. There are also other definitions based on perception or other theories of color. Unfortunately there is not just one definition of complementary color so you can't way that one is "right" and another "wrong".

Q: What colors do the three primaries make?
A: The traditional three additive primaries of red, green, and blue make white when mixed together in equal amounts. The traditional subtractive primaries of cyan, magenta, and yellow (sometimes called blue, red, and yellow) make black (or at least a dark brown) when mixed in equal amounts. However, primaries aren't limited to these traditional sets and can therefore potential mix to other color combinations. It will also depend on the amounts of primaries used, so really almost any color could be made.

Q: Why is white light predominantly used in hospitals and other medical facilities?
A: Because white light will most accurately render the color of all objects. Colored light might make it difficult to perceive or discriminate certain colors and it is important to be able to see as many things as possible in a medical facility.

Q: Why are deep sea creatures colored the way they are?
A: From what I have seen, they are pretty much not colored at all. There is no light down there, so it wouldn't make much sense for them to have sophisticated color vision or any meaningful colors on their bodies. There is some vision going on since some of the fish have "glowing" parts, but not much. The colors you see in pictures of the creatures are probably just caused by the material that makes up their body (lots of transparent and brownish parts) with no specific purpose for the coloration. There is still very much that is not known about these creatures. By the way, fish that live near the surface have very sophisticated color vision, perhaps better than ours!

Q: What color is the sky at night?
A: The color of the sky is whatever you perceive it to be ... generally something close to black. However, the physical stimulus is still essentially the same as it is in the daytime, just with less energy. Since our rod system is responsible for seeing the sky at night, it is not colored. If our cones were sensitive enough to respond to the small amount of energy present, the sky would still be blue. In fact the physical stimulus for all colors is still there, it's just that the amount of light is reduced to the point that we can no longer perceive color. For example, if a photograph is taken with long enough exposure time the colors will look just like a daytime photograph. So in a way the "colors" are still there, we just cannot see them.

Q: What color is the moon?
A: It depends on how you look at it. If you were to bring a piece of the moon back to earth and look at it with other objects, it would appear nearly black, maybe a dark gray or brown. However, the way we normally see it, the moon appears to be white or very pale yellow. The reason for this is that it is reflecting some light from the sun (about 8%) and in the night sky that is pretty much the brightest object we see. When we see any light isolated in a dark surround it will tend to appear white (unless it has a very saturated color like a red light).

Q: Why is grass green, a banana yellow, water bluish-green?
A: There are many ways to answer this question. One could say that those objects are those colors because that's the way we perceive them, but that's not really very satisfying. They have those colors because of the way the chemicals in them interact with light. For example, the chlorophyll in grass reflects green light and absorbs blue and red. When a banana ripens, chemicals that absorb just blue light remain. Water is a chemical itself and interacts with the light to produce the blue color (helped out by light scattering from stuff in the water).

Q: How do color blind people view fireworks?
Q: Can color blind people see fireworks?
A: Sure, people with color vision deficiencies can see fireworks. They see the bright lights on a dark backround just like the rest of us. However, the colors they see will be different. In extreme cases they will only see light and dark, but most will see colors in a more limited range than those with "normal" color vision.

Q: Why does eye (iris) color appear to fade with old age?
A: I found a brief explanation online at wonderquest.com. Eye color is determined by the amount and distribution of melanin in the iris (melanin also gives our skin and hair its color). Apparently with age, the density (amount) of melanin can change in the iris resulting in the observed change in eye color. Similarly this can cause our hair to change color as we age. However, the perceived color of our iris does depend to a degree on having a dark area behind it and as we age the lens does yellow. That would make the area behind the iris less dark and therefore change the appearance of the iris. I would suspect that the changes in pigment density are far more important than changes in the lens, however. There are also other causes for changes in eye color that are mentioned in the linked column.

Q: What is light?
A: The official technical definition is "any radiation capable of causing a visual sensation directly". Light is electromagnetic energy that is visible to humans. The range of wavelengths is generally taken to be roughly between 380nm (violet) and 760nm (red) with the visible spectrum in between. Wavelengths just less than about 360nm are ultraviolet and just longer than 760nm are infrared.

Q: If people are affected emotionally by color, then are people with color blindness less emotional?
A: Not at all. Colors can influence our emotions, but emotions are very complext and caused by many things. There is no reason to think that anyone with limited color vision, or even no vision at all, would be less emotional than anyone else (at least not for those reasons).

Q: Do all colors fade at the same rate?
A: No. It would depend on how the color is made, what it is exposed to (light, moisture, heat, etc.) and how you measured "fading".

Q: Why is the sky all different colors?
A: Most of the sky is blue due to preferential scattering of the shorter wavelengths of light (blue). But this is also why sunsets are red (in that case we are seeing the light from the sun that goes straight through ... the blue is scattered off to the side) and why clouds are different colors (scattering of all wavelengths to amke white and reflection of the blue and red from the sky, sunsets, etc.). It is truly possible to perceive the sky as any color depending on the weather conditions, sun location, observer, etc.

Q: Are Angus bulls color blind?
A: The most recent research suggests that cattle, and I would assume that Includes Angus bulls, are color blind by human definitions. However, that doesn't mean that they only see in black and white. Instead they appear to have two classes of cones receptors (rather than our three) and thus likely to have vision similar to what we would consider red-green color blindness. So they can probably discriminate some colors, just not as well as color-normal humans.

Q: What colour jelly would melt faster? Blue or red?
A: It depends what you do with the jelly. In the dark, and assuming that the color has no other effect on the jelly, they would melt at equal rates. When exposed to light, the one that absorbs more light will heat up more and therefore melt faster. If the light was red, it would probably be the blue jelly. If the light was blue, it would probably be the red jelly. If the light was white, it woudl depend on the specific colors and probably be a toss up.

Q: Do objects that are the same color have the same chemicals (elements) present? For example if I looked at the chemicals in red paint would I find the same ones in a red flower?
A: Generally no. Simply put, there is more than one way to make the same color. For example, grass is green due to chlorophyll, but my color TV can make that same green color with a combination of red, green, and blue phosphors and a color printer can make grass green with cyan, magenta, and yellow inks or dyes that include no chlorophyll at all. There are lots of different materials capable of producing any given color.

Q: Why are the walls in schools painted with bright colors?
A: It probably has little real effect on learning, but is done because people believe that bright colors are enjoyed by children and stimulating. That might be true, but all that really matters is that the color scheme (including the lighting) is not distracting or boring to the students. If it is, there might well be other, more important, problems in the classroom.

Q: How does the color red work?
A: I've never seen a color work? Red objects look the way they do, because the tend to absorb the shorter wavelengths of light (blue and green) and reflect the longer wavelengths (red).

Q: All my life my favorite color has been blue, now as I age it seems to be red. What does this mean?
A: Nothing. Preferences change over time and color preference is like any other. I used to love steak and now I am a vegetarian. Steak is not at all appealing now. It is not at all unusual for favorite colors to change with our changing lives. In my past my favorites have been very strong and gone through the sequence from green, to orange, to gray, to red (my current favorite). I don't think there is any meaning there.

Q: What colors can humans not see?
A: None! Color is defined as a human perception. If we can't see it, then it's not "color".

Q: What colors do I mix to make blue?
A: It depends what you are mixing. If you are mixing cyan, magenta, and yellow dyes or inks, then you can make blue by mixing magenta (which aboorbs green) and cyan (which absorbs red). If you are mixing lights, it is more difficult since blue is at the end of the spectrum, but it would be possible to make a blue by mixing green and purple lights. It wouldn't be the most saturated red, but it could be done.

Q: How does a tv make purple?
A: A TV makes color by displaying varying amounts of its red, green, and blue primaries. Purple would be made from an approximately equal amount of the red and blue primaries. Since we are normally too far from the TV to see the individual color areas, we perceive the additive mixture of red and blue, purple.

Q: Would a dark colored M&M melt faster than a light colored M&M?
A: If they were exposed to light and it was enough to actually melt an M&M, yes. The darker ones will absorb more light (that's why they are darker) and therefore heat up more.

Q: If you mix red and purple what does it make?
A: It depends what you are mixing. If it is light, then you will get a purplish-red. If it is paint, probably it will be closer to the red. Of course this all depends on the nature of the materials you are mixing and the amounts of each.

Q: What does it mean when a crab has white eyes?
A: I have no idea. If anybody does, please let me know through the "feedback" page.

Q: Is there a higher percentage of color-blindness (or limited color perception) amongst people with blue, hazel, or other light-colored eyes?
A: To my knowledge there is no correlation between eye color and color vision defficiencies (color blindness). While both are normally genetic, or inherited, traits, they are not controlled by the same genes.

Q: What two colors mixed together make red?
A: It depends what you are mixing. If you are mixing cyan, magenta, and yellow dyes or inks, then you can make red by mixing magenta (which aboorbs green) and yellow (which absorbs blue). If you are mixing lights, it is more difficult since red is at the end of the spectrum, but it would be possible to make a red by mixing orange and purple lights. It wouldn't be the most saturated red, but it could be done.

Q: Why do certain objects appear white? And black?
Q: Why do we see black?
A: Why not? I guess you might think we'd see "nothing" since black often happens when there is no light in an area. In fact, if we are in an environment with absolutely no light, we don't see black! Black is a perceived contrast to white and when there is no light at all, there is no white, so there can be no black. Instead, what we see is a visually-noisy, kind-of-dark, gray. Our visual system works to perceive contrast. And black vs. white is one such contrast. We see black because we see white and areas with relatively little light (compared with the surroundings) will look dark, or black. Another interesting feature of our visual system is that perceived contrast increases with the amount of light. So if we take a scene and illuminate it with more light, everything does not get brighter. Instead the light objects look brighter and dark objects look darker!! That's more perceived contrast between white and black.

Q: Who invented the color red?
A: Color is a perception, so colors weren't really "invented". Rather our ability to produce these perceptions evolved. You could look into who invented certain red colorants, but that wouldn't give you a single answer and certainly the color name "red" (or versions in other languages) was used long before man-made colorants were created. It turns out that "red" is usually the first color name to develop as a language evolves (after light and dark).

Q: What is the color wheel?
A: There are many color wheels out there that are based on different types of theories. The idea of a color wheel is that it puts hues in a logical order and provides some indication of what might happen when various colors are mixed. Color wheels help people create, organize, and describe colored materials and color perceptions.

Q: Why does the color black absorb heat faster than other colors?
A: An object is black because it absorbs most of the visible energy (light) that falls on it. This energy is then converted to heat. Since a black object absorbs more light than objects of other colors (otherwise it wouldn't be black) it also heats up more. Absorption of infrared energy is very important for heating up as well and it just happens to be more likely that objects with dark colors will also absorb more infrared.

Q: Why are people attracted to different colors?
A: For the same reasons we are attracted to anything. We all have our preferences based on previous experiences. We are all individuals and have developed different preferences. Some prefer red, while others prefer blue. Blue happens to be the most popular "favorite color" in North America. Maybe that's because the sky is blue on pleasant days???

Q: How do opaque objects get their color?
A: They are opaque because they do not allow any light pass through. Thus, we see these objects because they are reflecting and scattering some of the light that falls on them. If this reflection and scattering happens in different amounts for different wavelengths of light, then the object will have some hue (if not it will appear white, gray, or black ... which are still colors). Any light that is not reflected or scattered must have been absorbed and it is this absorbtion of different wavelengths that usually produces colors. The absorption properties are determined by the chemical properties of the material (what it's made of).

Q: Why do I see a finely rendered color space, with what seem like the appropriate pastels, etc., when I view a tristimulus picture made with lasers, where the three illuminants are monochromatic?
A: This is because our eyes cannot tell how a stimulus is made. We have three types of cones in our retinas and as long as the energy absorbed in the three types is equal for two stimuli (e.g. a pastel made with paint and illuminated with daylight vs. a pastel made with three lasers, then the colors will match. This is the definition of metamerism, which is the basis of modern colorimetry.

Q: If the 3 TV primary colors are blue, red, and green; what color of the three do humans see as the strongest or most easily?
A: There is no relationship between the two. The TV primary colors were selected to provide the largest gamut with the fewest primaries (and least amount of energy). They do correlate very approximately with the peak responses of the three cone types. However, the most easily seen colors are those that contrast most with their background. For example, it is very easy to detect white on a black background. Contrast is more important to our visual system than the color of an isolated stimulus.

Q: Tell me something trivial about color?
A: There are apparently fewer than 20 words in the English language that have no word that rhymes with them. Four of those are the color names orange, purple, silver, and olive. Beware when you are writing your next poem about color science.

Tree Growing From Rock in Algonquin
This tree illustrates a marvelous adaptation. It started growing on a rock, so it had to send its roots on the outside of the rocks down to fertile ground.

Colored Shadows at The Exploratorium
Here is a picture of my shadow (while taking the picture) in the "Colored Shadows" exhibit at The Exploratorium in San Francisco. Three lights are projected on the wall, red, green and blue. Yet the shadows are cyan, magenta, and yellow. Can you figure out why? Can you figure out where the red, green, and blue lights were?

Various Eyes from Exploratorium Book
This is a shot of the inside cover of "Exploratopia", by Murphy, Macaulay, and The Exploratorium, that shows such a wonderful variety of iris colors and eyes from different species.

My Full Moon 800mm
This is an image of the full moon taken with one of my digital cameras, and 800mm telephoto lens, and a nice tripod! It is intersting to ponder why the same side of the moon always faces the earth. That means the period of the moon's rotation is identical to the time it takes to orbit the earth. Coincidence?

A Nice Rainbow at Niagara Falls
If there is sunlight and water droplets in the air, then there is a rainbow somewhere. It's just a matter of lining up the angles so you can see it. I shot this one from the top of Niagara Falls.

Old Faithful Contrast Circles
Notice the strange circles in the sky. I took those circular areas and simply flipped them vertically in their location in the sky. It is amazing how much visual contrast is provided by the slow gradient of the sky and the strange appearance of depth that happens from flipping the circular areas over.

Purple Sea Star in Maine
We found this 9-armed sea star (commonly called "starfish") off the coast of Maine. They often have many more than just 5 arms and they come in a variety of colors. It turns out their color depends on what they have been eating.

Subtractive Colors
Cyan, magenta, and yellow are typically considered subtractive primaries. This is an actual photograph of overlapping cyan, magenta, and yellow filter disks on a light table. Where cyan and yellow overlap, green light passes through. Where yellow and magenta overlap, red light passes through. Where magenta and cyan overlap, blue light passes through. And finally, where all three overlap, no light passes through and we have black.