Personally I like black, blue always looks fake to me and takes away from the true colors of the fish.
Heres what I mean.
Nosferatu bartoni with blue
Nosferatu with black
another example Nandopsis haitiensus with black
Nimbochromis on a brown background
same species on a black background
Got my black background today, just taped it up to get a general idea of how it will look. I think it looks good. Ill give it a few more days before i stick it on.
Sorry for the ****ty angles, i was getting a glare