What are the colors?
Does light create them? Is it the material? Or are they just concepts that we have dressed up in our head (which would explain the famous black-blue / white-gold image)? Actually… all three are true!
Well, let’s start with the light. “Pure” light, that is, white light, is composed of various wavelengths, each of which corresponds to a color. However, we cannot see, with our eyes, all the existing colors (such as infrared, ultraviolet, gamma rays, x-rays, microwaves and radio waves), and we are therefore able to see only some of them, the wavelengths that make up the visible spectrum.
At this point we proceed with the material. Each object is made up of molecules called chromophores, which absorb light waves… except one, which is rejected and reaches our eyes. For example, if we take an orange, and we see it as orange, it means that the chromophores of that orange absorb all the colors of pure light except, in fact, orange, which bounces and reaches our eyes. So, are oranges orange or not?
In our retinas we have neurons called specialized photoreceptors to analyze the wavelengths of the visible spectrum that reach our eyes: they are called rods and cones. We don’t care about the rods at this moment, because they only deal with white, black and gray scales (thanks to which we can also see at night, with dim light that cannot make us see “colored” objects). Cones, on the other hand, are divided into three types: S (“short”, sensitive to blue), M (“medium”, sensitive to green) and L (“long”, sensitive to red). Each of these is more or less stimulated by certain wavelengths, sending the data to the brain which “adds” them and processes the color. For example, for the orange, the blue cone will not have been stimulated almost at all; the green one a little more; but the red one almost to the maximum: the brain collects these data, processes them and understands that the color in question is orange!
And the yellow? Shouldn’t that be the right primary color, instead of green?
Well, our M cones work with green because it has a wavelength halfway between red and blue. But there are people, more specifically women, who also have a fourth cone: the yellow one. This condition is called tetrachromacy, it’s due to a variation in the X chromosome and those who have it can see thousands of shades more than normal people.
But the colors we see do not depend only on wavelengths, otherwise we would not be able to explain how we see magenta, which does not have any.
Kitaoka Akiyoshi is a Japanese psychology professor who studies visual and perceptual illusions who invented the “color constancy” theory. According to him, objects always appear to us their own color even when subjected to different types of light. For example, thanks to this ability we do not go crazy in recognizing the same orange at sunset rather than at dawn, even if in fact it assumes objectively different colors. If we didn’t do this, we would not have been able to orient ourselves or to know that we aren’t cyanotic just because we are underwater.
And in fact, we also see magenta, which does not exist in nature. It doesn’t have a wavelength; it doesn’t really exist. And it is not the only one, there are many other colors that do not have a wavelength that we can see, however: we can distinguish brown from orange, even though they have the same wavelength.
Magenta is not in the visible spectrum, when it should be either before red or after purple (being a mix of the two).
In fact, if between blue and green there’s cyan and between red and yellow there’s orange… then the magenta (blue + red) should be in the middle, that is, where there’s the green. But our brain thinks in opposites: where there is cyan there cannot be red, where there is blue there cannot be yellow; and then if in the spectrum the opposite of green, which is in the center, is not there… then the brain creates it: magenta.
In the end, this color doesn’t exist except in our heads.