I bought a background from PetSmart; they have double-sided ones and I've seen plain black. Mine is black with some driftwood branches running through it. I have mine against a wall too (and thought of a background after I set up the tank and filled it lol) but I managed to do it. I measured the tank's front from side-to-side and up-and-down, then measured it out on the background and cut it to the right length, width. I bought some SeaClear background stuff; you smear it on the background and then adhere it to the back of the tank. It doesn't fully stick so you can slide it around and position it, then just press a credit card or ruler on it to smooth out the bubbles.