How We See Color
One of the most mind-boggling parts of color theory is the observation that two different colors of light, when mixed, can create a new color. For instance, red and green light shining together, like from the pixels of a TV or computer screen, give the perception of yellow. This is a phenomenon called “additive color” mixing, illustrated below:
It turns out that the word “perception” is the key there. Different colors of light each have their own characteristic wavelength and the yellow coming from your monitor is still red and green wavelengths traveling simultaneously toward your eye. The perception of yellow, or any “in-between” color, comes from simultaneously activating more than one kind of “cone” color receptor in the back of your eye. See how yellow, which by itself would have a wavelength of around 570 nm, falls between the red and green cone receptor ranges:
That explanation up there is thanks to another great video by the folks at TED Ed. Check out my previous vision posts here, including OK Go and Sesame Street explaining primary colors, a fun test of your ability to tell colors apart, and an exploration of the idea that Vincent Van Gogh may have been colorblind.