COLOR

When studying color, you are learning about the eye, not about light. When we meet up with beings from elsewhere in the universe, we might find that their science of color is completely different.

Because of the signals from your eyes to your brain, the system works as if there are red, green and blue signals only. I say "as if" because it is a little more complicated, involving adding and subtracting signals, but we don't need to get into that. White is approximately an equal mixture of the three, so Caucasians are the colored folks. If you mix colors by shining them on a surface, it needs to be a white surface or else all of this is nonsense. But you are observing another way of mixing right now. I bet there is white on your computer screen, and if you get a powerful magnifier you will see red, green and blue dots. A drop of water on the screen could do the job if you don't have a powerful enough magnifier.

The dots are so tiny and close that the naked eye does not see the individual dots, so they are blurred together and it is the equivalent of color mixing.

When you see yellow, the eye is feeding the brain with equal amounts of red and green signals. (If the ear-brain combination worked this way, our music would be completely different. Play the notes c and e together and you would hear d.) There is a single wavelength of light that (yellow) that sends the brain equal parts red and green, and your eye can't tell the difference between that and the equal amounts of red and green wavelengths.

From what I have said so far, you might have the impression that any two wavelengths mixed together look like a wavelength half-way between them. True if they are close enough, but not if they are near opposite ends of the spectrum. Red and blue together look like a color which cannot be replicated with a single wavelength: magenta, a reddish purple color. So people concocted a color triangle, which says something about the eye-brain combination, not about light.

It turns out that if you put red, green and blue (rgb) on the corners of a triangle, with white at the center, yellow halfway between r and g, cyan (teal) halfway between g and b, and magenta halfway between b and r, that is pretty much it. Mixing any two of these lights yields a color in between.

The color triangle below is incomplete. The colors should gradually go to white as you approach the center.

Mixing pigments (e.g. paints) is different, because they subtract colors by absorbing light. What you see is the reflected light, and absorption robs from the reflection. Green paint, for example, absorbs more and more light as the wavelength gets further from green, so white light shining on a green surface results in reflected light that is mostly green.

Mixing equal amounts of red, green and blue paint will result in a very dark color, because it will absorb all wavelengths (but probably not 100% of any particular wavelength).

The subtractive primary colors are the complements of rgb: cyan, magenta and yellow.

Now go back to the main junk on waves.

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