Section 508 Web Standards
(c) Web pages shall be designed so that all information conveyed with color is also available without color, for example from context or markup.
What does it mean?
Color cannot be the only way used to convey information and instruction because persons with color blindness or with low vision will not be able to use the page.
How to evaluate
People can understand the information on the web page without relying on colors. Instructions do not require the reader to check all items listed in one color (e.g. check all items in "blue) or fill in fields that are displayed in one color (e.g. fill in all items in "blue"). The page is readable on a black and white monitor and when printed from a black and white printer. Links displayed in different colors are also underlined or are differentiated from the content.
For more information
Design Resources