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.

That's why you don't just use colour for identification. E.g. include a warning icon next to a button/element in addition to using a warning colour.

should be, but then you will upset all the marketing folks and their brandings.

[dead]

Riddle me this - why would you want to disable something that increases usability of an application? (Yes, this is a loaded question - I never said these features are bad, just that usability and accessibility are sometimes at odds with each other.)

You might be the kind of person who does benefit from accessibility features such as larger font size. On the other hand, I'm not; I can read 10pt font on 100 DPI display just fine, without glasses. I'd rather have an extra column in table view visible without scrolling than larger letters, but for you the tradeoff might be different. That's why it's accessibility and not usability. Usability would be if the bigger font didn't push anything off screen, then of course it's better to make it bigger.

Everybody has some minimum text size they're comfortable with. If you make the text bigger than that, they're forced to scroll unnecessarily, which is less usable. But the size differs from person to person, so it should be configurable. You get this automatically with web browsers and most GUI frameworks if you don't go out of your way to break it (just stick with the default font).