I've been working on some accessible designs for a government client, and I've noticed that the WordPress admin pages, the WordPress.org theme, and many wordpress themes do not have sufficient color contrast to meet WAI guidelines.
Probably not a big deal with individual themes, but the admin theme is an issue for all. I can't seem to find a WordPress.com theme that passes muster. (Not that that matters here.)
If you want to see what I'm talking about, check it out with the Juicy Studio Accessibility toolbar: