We've all been told that the colors of the rainbow correspond to different wavelengths
of visible light - red, orange, yellow, green, blue, and violet. Where's pink in that list?
It's not there. There's simply no pink light.
So where does pink come from? It turns out that pink, (or magenta, fuchsia, or whatever
you want to call it) is actually a mix of red and blue light - light from both ends
of the rainbow that our brains see as one single color.
If you try to roll up the rainbow to make a color wheel, there'll be a gap between red
and blue. That's where all of the rest of the light in the universe is supposed to go
- radio waves, microwaves, infrared, ultraviolet, x-rays, gamma rays, and so on. But since we
can't see any of those wavelengths, we replace all that hidden grandeur with pink.
And speaking in terms of light, pink should probably be called "minus-green", because
pink is what's left over from white light when you take out the green.