|MadSci Network: Biochemistry|
Tom, Color in the cones is distinguished by several different closely related proteins called opsins. An opsin protein is attached to a molecule of vitamin A to form a molecule of rhodopsin. Anyway, normal people have 3 different opsin proteins which all respond best to a certain wavelength, or color, of light. The three colors which these three opsins respond best to are red, green, and blue. Each cone has only one type of opsin, so every cone is either a red, green, or blue cone. People who are color-deficient or "colorblind" are missing either one, two, or all three of their opsins, and so are missing one, two, or all three types of cones. This is pretty much a simplification. You're probably wondering, "If we only have 3 colors of cones, how the heck can we detect over a million separate shades and hues? And what about yellow?" The answers to those are a bit more complicated and get back into brain processing, so I'm not going into them right now. But if you want to know, just keep asking questions! Tom p.s. I got my info from "Biochemistry" by Lubert Stryer.
Try the links in the MadSci Library for more information on Biochemistry.