Related sites and products
Since I first posted this site in 1998, various other people have developed some tools along similar lines - sometimes based on what I've done, sometimes independently. This page has links to the ones I know about. I also include any articles that refer to this work. [I've checked the links in Oct 2010, and these work as of then]
YoYo design have produced a tool called nColor, which can be used on the web page or downloaded for use on the desktop. This allows you to choose background and text colours, useful for checking readability for your choices. It also has a switch to view the approximations for the three kinds of dichromatism.
Thomas Wolfmaier has written an article (Designing for the Color Challenged) which includes an applet that allows you to type in background and text colours of your choice. It then displays the transformed colours and their RGB values. Because it uses algorithms, it is not restricted to the web-safe colour palettes.
The Visibone Color Card and Color Chart display the standard web-safe palette, with a small copy alongside that approximates the colours as seen by a deuteranope. The Colorlab is a useful tool there for assembling a site palette, and screen clips can be transformed with my palettes to check for clarity in terms of colour vision.
Jason McNeill (from SmartShip.com) has developed the protan and deutan palettes for use in Homesite, based on the protan and deutan palette gifs on my Palette files page. He has given me permission to let you download his Homesite palettes from here as he doesn't yet have a site that offers them.
Can Color-Blind Users See Your Site? An article by Robert Hess for the Microsoft Development Network (MSDN), October 2000.
Adjusting for the Colorblind. An article by Ian Austin for the New York Times, 2 November 2000.
What Is The Best Text and Background Colours To Use In Website Design? A blog post by Shaun Anderson of Hobo Search Marketing.
Color Vision Confusion. From the Universal Usability in Practice site, a class project from the University of Maryland, May 2001. Offers visual design guidlelines for avoiding problems with colour deficiency. There are links to many resources on this topic, mostly since 1999.
(updated in Feb 2011)