It's actually quite hard to distinguish between the black and the maroon, especially since the two aren't together. Don't know what it's like with Original Blue and Liquid Violet, though. Never use them, doubt I ever will. And I'm too lazy to check.
If you to to the place in your user CP where you change your avatar, it tells you how big you can make it. I think it's like 150x150 but I can't remember.