Icon Fonts and contrast

[Gregg wrote in another thread related to WCAG extensions] can't extend this to ICONS unless you very carefully define icon icon art and figure out how to handle the fact that you can only have one color other than black and white and still have everything contrast with everything else.  Mathematically impossible.   You can try it.

Gregg, I am interested in your thoughts on why there is only one additional color available other than black or white - is this because the icons may be actionable?  I understand there are limitations in link text with different types of links such as visited, non-visited, etc. without other decoration -- is it a similar issue?

Jonathan