I just painted the back of my 55. I couldn't spray paint cause the tank is already setup and is indoors (obviously). I went to walmart and got Krylon Acrylic Latex "Gloss Black" and applied it with a foam roller. Came out perfect. The paint I used previously was rolled on as well, but it wasnt a deep black, more of a grey. Since it was latex based I was able to peel it off in one big sheet, so you are able to change it if you want. Make sure to clean the back, I used vinegar and it worked very well.