A fellow Pivot recently asked me about accessibility requirements around the use color with text in a page. Here is the answer I gave her.
Color itself is not as relevant as contrast ratio (for color blindness in particular). The contrast ratio rule is (according to WCAG 2) 4.5:1 for body text and 3:1 for large scale (minimum 14 pt bold weight or 18 pt normal).
A useful tool to check this is the HTML Codesniffer bookmarklet. You can run it in the browser to check for acceptable contrast. There is also a phantomjs runner for Codesniffer that you can use on the command line. The command line runner is especially exciting for its potential in automated accessibility testing.
