It’s true that color adds beauty to scenery, faces, paintings and so on; sometimes we use it as a signal like traffic lights or wire colors which helps the electrician connect them right. But evolution which created our senses, didn’t have much interest in beauty but mostly in surviving, and traffic lights or wires weren’t a part of the ancient life, why than, do we see colors?

Color helps us recognize different things faster and easier. When our ancestors had to escape lions in the jungle or find a fruit to eat, seeing colors was probably so efficient that it was “worth while” for evolution to develop it. even so it’s weird: color vision evolved again and again during evolution, a fact which points that “it isn’t so hard to do”, yet, not all animals see colors. Gold fishes, pigeons and squirrels see color, monkeys from america-don’t, and cats-only a little. If seeing colors has so many advantages, why than did evolution “abounded” it, or why so many animals don’t have it?

In evolution there’s always a balance between what you get and what you “pay” for it. color vision is “more expensive” than b&w vision: color vision requires many brain and nerve resources and we sacrifice some light sensitivity and vision sharpness. Sometimes the price is worth while and sometimes it isn’t. it seems that the efficiency of color vision is limited, as a matter of fact people who are color-blind(link) get along quite fine throughout life.

So what is ‘color’? we must remember that when we see something we actually see the light that comes from it-whether it’s reflected (a basketball) or emerged (fire) from it. Light is made of waves, it’s “quality” is the distance between sequent waves or ‘the wave length’.(light also has quantity which is the luminosity .) when the wave is “long” (70 millions of a centimeter!) we see red light, when the waves are “short” (40 millions of a centimeter) we see blue and purple- all the other colors are at the range between. White light (sunlight or lamplight) is a mixture of all wave lengths. A tomato swallows all the range off short waves from the white light which is beamed at it and the reflection our eyes see is only the longer waves so we see the tomato red.

Longer waves than those which enable vision are called infra-red, we can’t see them but we can feel them as heat. these waves are reflected from warm objects and there are snakes that can see mice at night by detecting infra-red waves. the waves that are used for radio and television transmission are of the same kind only even longer than infra-red. Waves shorter than blue are called ultra-purple waves and there are some insects that can see them, meaning that they see flowers different than we do. Very short waves can pass threw different materials and are called x-rays or roentgen rays. All these waves are called ‘electro -magnetic-waves’.

Infact, the connection between the wave length (which is a physical attribute of light) and the color (which is the sense of the light hitting our eyes) isn’t a non-breakable connection: the same light can make us see a slightly different color in different conditions. for example, a purple object would look a little red on a blue background and a little blue

How do we see color? First, how do we see at all? Our eyes record shapes and objects like a video camera, but the brain has to make sense out of this recording, recognizing it and remember these objects and shapes- this is what we call seeing. The eye lens  (like the camera lens) creates a shape on a “screen” which called retina. The retina converts the shape into electric signals that the brain can understand. The retina plays a main roll in color vision. it’s made of three kinds of cells and each of them in sensitive to a different part of the color range, they are called ‘red’, ‘green’ and ‘blue’ cells.(infact there is a forth kind, but it’s responsible for the night vision, which is color blind.)

The brain compares the reactions of all three kinds of cells for each point on the butterfly wing for example, and thus it decides about the color- than the brain connects all the points he tested and makes an image of the wing. How does it restores and how do we recognize and remember the image- those are mysteries that awaits for the future research to solve. How can it be that using only three kinds of cells we can see thousands of colors? The relative reactions of these cells are the outcome of their great sensetivity to the length of the light wave that they recive, for example, a green light stimulates the ‘green cells’ much more than the ‘blue’ and the ‘red’ cells which are equally stimulate,  a slight change of the light “towards” yellow-green will change this balance and the reaction of the ‘reds’ will be stronger than the ‘blues’ reaction. our minds can identify the changes with great sensetivity and this fact enables us to see such a verity of colors. This is a remarkable achievement and we don’t know how exactly the brain does it. Using only three kinds of cells makes it possible to “cheat” the brain: many different combinations of wave length, picked correctly, looks like the same color: a combination of “red wave length” and “green wave length” will cause the cells to react the same as if it was only one wave length which is the average of both lengths, and they both will look yellow. That’s the base of basic colors: every combination of wave lengths, or every color of light can be produced by adjusting   the intensity of overlapping light beams which are red, green or blue. Color television, color printing and color photography, takes advantage of the fact that you can restore each color by combining the three basic colors: if you look close enough (maybe through magnifing lens.) at a television screen while it’s on, you can see thirds of strikes or points colored red, green or blue, lined up. The electronic parts of the television adjust the intensity of these points in a way that when we look from a watching distance (where you can’t see single points), the combination of the points creates the desirable color .