Color
When choosing text colors, remember that some users cannot distinguish color well or that some may have low-resolution monitors.
Contrast
When specifying text, background, link, and border colors, make sure there is enough contrast between the foreground and background colors. The most common color combination in print is black text on a white background. Although black on white is great for print, this combination is much less desirable for screen displays. Computer monitors display colors by mixing red, green, and blue light. White is the mixture of these lights at full intensity; therefore, computer screens radiate the most light when displaying pure white. Consequently, blocks of black text on white on a computer screen can be too harsh on the eyes. (The text color on this Web page is a dark gray.)
Highlighting
Do not rely on color alone to highlight elements or text. For example, do not use background color on a form field to indicate that the user must fill it out. A red asterisk next to required fields, for instance, would be more helpful. Also, if you use color to highlight text (for example, headers or terms), also use bold or italic formatting.
For more information about making your Web sites more accessible, see the Web Content Accessibility Guidelines, developed by the World Wide Web Consortium's Web Accessibility Initiative.