What can I add???

I've had my 50g up and running for a while and it is finally completely cycled. The stocking list is as follows:
7 yellow labs (2 males 4", 5 unknown 2 1/2")
15 Demasoni ranging from 1" up to 3 1/2".
5 Synodontis petricola, 1-2" still rather young. ( I think thats what they are. They are the "dwarf" catfish. rather expensive)
1 6" sailfin pleco (don't know if I'm keeping it, It came with a used tank I bought but I'm pretty fond of it.)

I'm looking for another species to add for more color. I have a blue background so when the demasoni swim above the rock work they get "lost" in the blue. I was thinking (I know Kim is going to kill me for asking again) about adding 4-5 Metriaclima estherae to add some orange to the tank. I don't ever intend on distributing fry, at least not from the labs or zebras, maybe from the Demasoni. From what I've read, the Synodontis, if not the other fish, are likely to kill off any fry that the labs or zebras spawn anyway. So, other than the issue of crossbreeding, will this combo work as far as agression goes. Of course I would try to weed out males to end up with 1 male, 3-4 females of the red zebras to minimize aggression. Oh, I almost forgot, its a 50g show (same footprint as a 55g), C-360 and penguin 350. Thinking of getting a second C-360 since "Kens Fish" has them on sale for $127, and getting rid of the P-350. water parameters are perfect except for low ph (I'm working on that). I keep up with weekly water changes. All of the fish get along great! Just looking for another fish that would stand out from the blue background other than the Yellow labs.
Thanks in advance :thumb:

Khris