Color, Web Accessibility, The University of Arizona

Requirements:

If color is used to convey important information, an alternative indicator is used, such as an asterisk (*) or other symbol. The use of a color monitor is required.
Color contrast is good.

Low Contrast Examples:

Enter this web site by clicking here.

Color Blindness:

One in ten males have difficulty seeing full color. Approximately 1 in 5 of the total population have some form of vision impairment including glaucoma, macular degeneration, cataracts, retinitis pigmentosa and corneal haze.

Vischeck
Color Blindness Test