Two very interesting and useful sites on the eye and color.

http://www.biologymad.com/NervousSystem/eyenotes.htm describes the structure of the eye and color vision. This one is fairly technical but is short and has good graphics.

http://www.worqx.com/color/color_basics.htm describes the three "additive" colors, which are what we see and how computer monitors work, and "subtractive" colors, which are used for printing. It also goes into length on hues, tints, complementary and contrasting colors, chroma, saturation, and much more. It's a bit lengthy but it's an easy read (not technical) and quite informative.