[BarbMazz]

I think I'd stay with a neutral sort of color that won't compete with the colors in the tank. Think about what sort of undertone it has, too, because that can affect the way colors will look inside the tank. Maybe a warmer tan/brownish undertone rather than a colder gray undertone?

Or, good ole black on the wall behind the tank so the tank will "pop", and the rest of the room in a neutral shade?