We personally like black backgrounds since the color seems to make plants stand out more and hides algae better.
An aquarium background is optional but nice to have since it hides the power cables and airline tubing from view. You can buy a background from the local pet store, spray the back panel of the tank with Plasti Dip rubber coating, or even tape posterboard to the aquarium. We personally like black backgrounds since the color seems to make plants stand out more and hides algae better.