I like black the best becasue it contrasts nicely with most of the colors of tropical fish. I think it gives about the nicest background to display tank inhabitants and think this is the main reason why you see black dominate. It makes the fish standout and grab you attention. I find blue to distract from a tank but that is really just personal opinion.
I use the cheapest black spray paint I can find. It is quick and really more user friendly in the long run. No tape, oil, air bubbles, etc... to deal with. Just mask of the sides and top and take your time. Runs look like crap. Do multiple coats if needed. I like to light from the front so I can see thin areas.