All my tanks have 3 coats of Behr on 3 sides and the bottom. Miranda/Chicago Discus told my wife she does 3 coats, so that somehow became an expectation. The painting was done 5 years ago and I haven't had any problems. All the wires and tubes are hidden and I don't have to deal with flimsy backgrounds. As for color, it's a matter of priorities. I used a light blue which contrasts with discus colors (also what Miranda told my wife). Black also works except it's impossible to photograph the fish without supplemental flash, although altum angelfish look spectacular on a black background.
I don't think black is a problem on the bottom, although any color would work. You generally don't see the bottom of the tank unless you're standing right next to it. A roller will create a smooth coat, while brushes will create patterns. I've seen one person brush paint on, but using very little paint, to create patterns on the bottom. Some people have found paint that create a pebble pattern, which would be nice and hide fish crap.