What color is that?
It isn’t violet and it isn’t purple.
And why isn’t it in the rainbow?
Doesn’t the rainbow contain the whole color spectrum?
The short answer is that magenta doesn’t actually exist. (Well, none of the colors actually exist, but we’ll get to that in a little bit. Magenta doesn’t exist in an additional way. Now that’s real commitment to not existing.)
Your eyes contain three kinds of cone cells whose job is to detect certain wavelengths of light. One of these sees only blue. Another sees only green. The third sees only red. There are no cone cells to see yellow, purple, orange or any of the other colors.
Cyan_Yellow_Color-Spectrum_780
Mix any two colors on the spectrum and you get the color in between. (Keep in mind that we’re mixing light waves, not paints, inks or dyes.)
Mix green light and blue light and you get cyan, the color in between.
Mix red light and green light and you get yellow. Again, the color in between. Here’s what’s happening: the wavelength of yellow light is close to green and it’s also close to red, so both your “green” and your “red” cones send a partial signal to your wonderful, amazing brain. It somehow realizes these lightwaves are in between the wavelengths of red and green and BINGO! You see yellow.
Now take a look at the extreme ends of the spectrum where the shortest wavelengths are blue and the longest are red. If your blue cones are sending a partial signal and your red cones are sending a partial signal, this should mean you’re seeing the color in between blue and red, right? But green is between blue and red! And the eye has dedicated cones for seeing green!
What your brain “sees” in this instance is magenta, a completely imaginary color. If your brain had a name for magenta, it would probably be “the absence of green.”
Roy H. Williams