Comment by Xirdus

Certain types of colorblindness combined with certain colors makes text much harder to read than black-on-white. If you limit yourself to just universally readable colors, you're heavily limiting the number of different categories you can highlight. There's also the matter of screen real estate - duplicating info isn't helpful for people who can deal with colors just fine. I'm not saying it's a srong thing to do, just pointing out accessibility and usability are different things.