The Law
Section 508 Part 1194.22 Subpart c states:
Web pages shall be designed so that all information conveyed with color is also available without color, for example from context or markup.
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.
What to Do
People need to be able to understand the information on the web page without relying on colors. Instructions should 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 should be 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.
This might be most relevant when developing accessible atec:Forms