Chong suggested changing the font-lock-* faces colors, see http://lists.gnu.org/archive/html/emacs-devel/2009-07/msg01577.html.
I checked the WAC guidelines at http://www.w3.org/TR/2008/REC-WCAG20-20081211/#visual-audio-contrast-contrast and wrote a file for checking Emacs font-lock-* face colors:
This file contains Chongs suggestion and a test of the contrast they gives. I have also added my own suggestions. To see those suggestions, load the file and do
M-x test-font-lock-colors
You are welcome to add your own suggestions to this file.