Color blindness

Ishihara test, a color perception test
for red-green deficiencies

Recently I was tasked with redesigning a report in a way that would make it friendlier for people who can't tell apart red and green. The report provides information in a tabular format, using colors to provide visual cues about the data.
For the rest of us, all colors are made of 3 components - red, green and blue. Microsoft's page on color blindness shows how other colors are composed from the three. It also goes to show how different colors will be perceived by people with color deficiencies.
In order to adapt the existing web page, while preserving the user experience of existing users, I'm going to tweak the colors used.

There are some resources available on the web to aid in the task:

• Choosing safe colors - this page provides a sample selection of 10 distinguishable colors, together with a hint how they could be perceived by people with color deficiencies
• Websafe colors  for color-blind people - this page lists a set of colors, and also links to Color Oracle, an open-source color blindness simulator
• A nice theoretical background is provided on Designing For, and As, a Color-Blind Person

And finally, there's always the option of using other cues (instead of or together with color) to denote some properties of the displayed information.