Is there a prefered color that people use that makes the fish really stand out?Is there some kind of fish-safe latex paint that I could put on the back of the tank?
Not sure about paint, I use poster board outside the tank. I'd go with a black background to make your fish stand out. I used to like blue, but now I think it better suits marine tanks rather than freshwater.
I painted the back of my tank (on the outside of course) with cheap black spray paint. It turned out awesome. Much better than messing with a background.
I prefer black as well, although I have dark blue on my large saltwater tank. You don't need any specific "fish-safe" paint since the fish won't be touching it- you can just tape it carefully to avoid over spray into the tank, wait for it to dry, and there's your background!