I tried putting the background on in the dark, it worked fine until morning. Although Gussy wasn't scared, he did get a bit upset at the back of his tank being black. He constantly attacked the back wall, splashing several gallons of water out of the tank. I decided to forgo a background until I move him to a bigger tank. I'm guessing that being in a completely new environment will keep him from being a butthead about the background.
For some reason Gussy's tank water is pretty murky after the 25% water change, with a thin layer of slime on the inside tank surface. I'll keep changing 3 to 4 US gallons out every morning, it should clear up in a couple more days. Hopefully the medication will have done it's job and his fins will start growing to their full, proper length and size. I'll post a couple pics once the water clears up and certainly a bunch if his fins start growing (keeping fingers crossed).