Algorithm

Other Screen Filters

Allow users to simulate color blindness while working in any program.

xScope
xScope has live simulation of various types of color impaired vision. Commercial, Mac only.

ColorDoctor
This Windows XP program allows the user to move a filter over the screen that simulates color blindness.

Sim Daltonism simulates color blind vision and displays the results in real-time in a floating palette. Freeware. Mac only.

Application Plug-Ins

Extend the functionality of their host program to simulate color blindness.

Vischeck offers Plug-ins for Photoshop and ImageJ to simulate color blindness. You can also convert raster files and web-pages. Freeware. Windows and Mac.

Assistive Software

These "screen readers" manipulate the computer display to increase contrast for hard to distinguish colors. Helpful for understanding complex photos or graphics where component colors have poor contrast (useful for normal vision viewing, too).

eyePilot
Great for hard to read maps and diagrams. Floating, movable filter window helps color blind users by graying out non-target colors,  flashing target colors, will identify selected colors by name, and cycle through a variety of image adjustments that change color and contrast. Shareware for Macintosh and Windows.

Visolve
The Visolve Deflector is a floating, moveable filter window that allows the user to lighten or darken problem colors. Includes unique "hatchure mode" useful for reading charts and maps. Will also filter entire screen using "toolbar" mode. Macintosh and Windows. Mac version includes a Dashboard widget.

Further Reading

Wikipedia is a good starting point for learning more about color blindness.

A collection of links on Color Blindness and Color Deficiency.

ColorBrewer is an easy-to-use online tool designed to help people select good color schemes for maps and other graphics.

ColorSelector helps you pick two colors with good visual contrast for people with normal and color blind vision. Freeware for Windows and Mac.

The W3C provides a formula for determining whether two colors have sufficient color contrast.