Color Deficiency

Info on the 3 variations: http://www.iamcal.com/toys/colors/
Wiki page: http://en.wikipedia.org/wiki/Color_blindness

Visual test: http://www.lensshopper.com/eye-disorders/color-blindness.asp#test

Another test: http://www.color-blindness.com/color-blindness-tests/

Good site for general info and links: http://www.toledo-bend.com/colorblind/Ishihara.asp