I had a convict alone in my 6.6 gallon bookshelf aquarium, but his color looked pale; the bars and stripes on him were really, really light. I put him in my 55 (but I'm swapping that for a 20) and his colors practically immediately brightened up. I tend to think it's because of the white substrate I had in the bookshelf. I have blueish-green gravel in the 55. Could that be the culprit of his paleness? I plan on painting the back of the bookshelf ocean blue, should I also change the substrate to bring out the color of the fish I will place in there temporarily?