Well, you have a few options to go here.
in a 50 gallon i personally keep (and i know i am gonna get "what the heck are you doing?? You can't keep just 4 together!! You need more!!) ......
4 Ps. Demasoni (blue/black coloration)
6 Metriaclima heteropictus "Msobo Lundu Island"
9 Ps. Salousi
3 BN plecos
Also somewhere in the tank is 3 kuhli loaches (i know ... i am amazed at how they are surviving!!! Mostly cause they dig into my gravel)
I have added them all together (the cichlids that is) because my tank is VERY mature and could handle the bio-load (not to mention that i have an Ehiem 2213 and 2 AC 110's on it)
what i like about my mix is that all the cichlids are mbuna.
The Ps. Salousi males are a nice blue (similar to Demasoni) ... the Demasoni are REALLY a vibrant blue coloration.
The Ps. Salousi females are a nice yellow ... not as neon as yellow labs, but pretty damned close!
the Metriaclima heteropictus "Msobo Lundu Island" (rarer cichlid i ran into) are quite interesting as well. The males are this blueish/whitish color and the females are this golden color with a neon yellow fin to it.
You can see photos of my tank here in my Photo Gallery located at
http://www.aquariumadvice.com/photopost/showgallery.php?cat=500&ppuser=8018
