Ever since I’ve been a little kid, I’ve been thinking about our perceptions we get from our senses. Thinking about if other people saw the world as I did. As a kid you often feel misunderstood, because as a child you seem to see things that other people don’t see. And children aren’t taken very seriously anyway, so no one believed me or took note of my perceptions.

Bifocal insect eyes

I often thought about what it would be like to see the world through someone else’s eyes. Animals were a big interest area for my young and still evolving curiosity. I imagined to have eyes of an insect, watching the world through hundreds of lenses. What would it look like?

Though, even simpler things excited my imagination. I would often ask if a person saw the things I saw, explaining in great detail how I perceived it – just to know if I could see things other people couldn’t.

Colors are precisely such a thing. I wondered if everyone saw the world in the same way. The same grass that everyone can see might have a different color for every other person. Because when I say the word “green”, your brain will pop-up a color that you call green, which in my brain could be blue – it’s just a name, not the color.

Wavelengths and rainbows

Light Dispersion

As we all were taught in school that Sir Isaac Newton found out that a glass prism could split white light apart into it’s consistuent colors. Light consists out of very small particles called photons, and these photons have a “wavelength” that corresponds to a certain color. White light is made out of a spectrum of these wavelengths. Billions of these photons, with different wavelengths our eyes can see, combined make white light.

So light of a single wavelength corresponds to a single color. The brain just translates wavelengths into colors somehow. If you look at a rainbow, it’s the same natural phenomenon. You’ll see all the natural colors that make up white light.

But these are just the “natural” colors. Let me explain…

Mixing colors

At school we’ve learned that adding all colors of paint will produce the color black. Since we’re dealing with light, we have to use additive color mixing. It means that if you add up all the colors, you’ll get white.

Adding two colors of light (two wavelengths) will produce a new color. We are going to make a few mixtures to see what colors we can make.

Green and red make yellow.

Blue and green make cyan.

Blue and red make green?

Blue and red make green? That’s not what we really should get! We should get pink. But where is pink in our spectrum? It’s not red, it’s not violet… It’s not on the spectrum at all!

So, a wavelength of a photon does correspond to a certain color – but we can’t produce all colors the eye sees with a single photon wavelength. There are natural or “pure” or “monochromatic” colors (the rainbow colors) and “unreal” colors, only existing in your brain. It means that at least two wavelengths must be mixed to create all the colors the human eye can see, in this example: pink.

Colors in the brain

The rules for creating these “unreal” colors is to mix the “real” or “monochromatic” colors that hit your eye. In the 1920s W. David Wright and John Guild both conducted experiments designed to map how the brain mixed monochomatic light into the millions of colors we experience everyday. They set up a split screen – on one side, they projected a “test” color. On the other side, the subject could mix together three primary colors produced by projectors to match the test color. After a lot of test subjects and a lot of test colors, eventually the CIE 1931 color space was produced.

This is the CIE 1931 color space; a map of the colors the brain can produce by mixing the monochromatic colors. On the curved border we can see numbers, which correspond to the wavelengths in the spectrum we saw earlier. We can imagine the spectrum bent around the outside of this map – representing “real” colors. The inside represents all the colors our brain produces by mixing – the “unreal” colors.

Now let’s try to mix the colors again!

Blue and green make cyan.

Green and red make yellow.

Blue and red make pink!

Pink is not on the curved line, thus is it purely a construction of your brain – it does not reflect a wavelength of a single photon.

Color and reality

Firstly, photons with certain wavelengths correspond to specific colors. These are the monochromatic colors. Variations can be made by mixing these colors. However, there are colors the human eye can see that do not have a specific wavelength. These colors are brain-constructed colors. The inner area of the CIE 1931 color space is purely a mixture of monochromatic wavelengths that the mind converts to different colors. It resembles the natural spectrum of light you saw earlier in this post, but is not the same.

The brain calculates these “unreal” colors by averaging the wavelengths of photons, producing a new color that is not based on the natural spectrum of light. It is an example of what philosophers call qualia – a subjective quality of consciousness.

Is color real? Well it’s not yet specifically defined wether it’s real or not… The real thing I learned is that  it is possible for people to see different colors which do not exist. And I know that children might see things that we as adults cannot perceive. I’ll pay more attention to the curious questions of children in the future.