Do not rely on users' perception of color to differentiate items on the page. For example, when asking for input from users, do not write "Please select an item from those listed in green." Instead, ensure that information is available through other style effects (e.g., a font effect or in graphics, different shapes) and through context (e.g., comprehensive text links). 

To test whether your document still works without colors, examine it with a monochrome monitor, print it on a black and white printer, or view with browser colors turned off. 

It is recommended that you use style sheets to specify text and background colors so that users can override color choices with their own style sheets. 

Rationale:

If color alone is used to convey information, people who cannot differentiate between certain colors and users with devices that have non-color or non-visual displays will not receive the information.