An often overlooked aspect of usability is the web through the eyes of the color blind. I've taken to running many sites through these filters and it's amazing how terrible some are.
(1) My favorite and most useful online tool to see color effects for Protans, Deutans and Tritans. There are also other helpful tools on screen. I've used this site regularly during development to see the side effects.
Since many of you are used to what Sitepoint looks like on a daily basis, see what it looks like here (Good Job!). http://colorfilter.wickline.org/index.cgi?a=1;r=;l=9;j=1;u=www.sitepoint.com/%3FSID%3D7aac32cdc04ced10e21ca0438a99bb02;t=p
(2) Simulations and Daltonize corrections:
(3) Short but informative article on color vision and color deficiency: