I think it depends on what fish you are keeping and your own personal preference. I have tried several different backgrounds. I tend to like the darker ones because I think they help bring out the colors of the fish. My current background on my 125 has alot of black with roots and rock. If you want the fish to be the main attraction then go with black. If you want a scene more natural, and maybe like your fishes normal habitat, then go with a darker picture background.