Check out the 50G build thread link in my sig... that tank has a solid white background on it...
Honestly, i'm currently using 3 types of backgrounds on 3 separate tanks, 1 has a 3D background, 1 is black, and the other is white... personally i almost prefer the cleaner look of the white background, but it really depends on what you are trying to achieve with the tank, as to what type or color background you would want to use...