Strange that there is a node for color, and not colour. Some sort of compromise must be made here.
Anyway, color is perceived according to radiation's wavelength. Red has the longest waves, purple has the shortest. Everything else is in the middle, amazingly enough.
The phrase "of color" usually refers to non-Caucasian people, which is sort of strange, since Caucasians are sorta pink, and pink is a color, too.