Making Your Web Colors Visible for All - Five Color Accessibility Tools
From: Sitepoint Blogs
By: Jennifer Farley

If you are designing, or re-designing your web site, it is time well spent
running your website through the color accessibility tools below to ensure
that your site can be seen correctly by as many people as possible. Most of
these tools use WC3 guidelines to perform their various operations. If you
can actually read and understand them, the Web Content Accessibility
Guidelines (WCAG) 2.0 requires, amongst other things, that there is
sufficient contrast between text and background color. For a person with a
color disability, the colors used on a web site can mean the difference
between being able to read text and images or not. 1 in 12 people have some
sort of color deficiency. 

Read the entire article at:
http://www.sitepoint.com/blogs/2009/08/20/color-accessibility-tools/ 

Links:
Web Content Accessibility Guideelines
http://www.w3.org/TR/WCAG20/