So you just want any blue/black fish to go with those you already have?
Does it have to be a cichlid?
If you are prepaired to add 3 more tiger barbs (that'll reduce the chance of them nipping new additions), that opens up your options and there are countless blue and black possibilities.
The one I would reccomend for you is an opaline gourami (trichogaster trichopterus color morph). You should stick to either a single male OR get 3 females. The males have longer fins, a pointier dorsal and are much more 'stream-lined' in appearance when compared to the 'deeper' and wider females. The reason you should keep the male alone is that they can be quite aggressive towards their own kind or other gouramies. The females do better in groups but keeping just 2 can still be a problem - that's why 3 is best to split up any aggression. Once you have this species of gourami in, don't add any more gouramies. Also, having a planted tank helps. This fish gets to 6" and spends most time in the upper layers. Avoid adding any more top-dwelling species once you have some of these in.
Alternatively, melanotaenia lacustris (turquoise rainbowfish) gets to 4" or so. However, as this is a schooling fish, you'll need at least 6 and that'll mean your tank is fully stocked if you choose these. Their size means they can handle boisterous tankmates but nothing aggressive. You wouldn't be able to add anything else though anyway. They are bright blue (once settled - they'll appear dull in the LFS) but have no real black on them. They are still my favourite rainbow though and absolutely lovely.
Besides the turqoise rainbow, there's the smaller red and blue melanotaenia praecox. this dwarf neon rainbowfish, as it is often called, gets to about 2.5". It is also a schooler so keep at least 6. These are peaceful fish but should be fine with the other fish you have provided you keep them in a large enough school and, prefferably, if you also add 3 more tiger barbs to decrease their nippiness. Though they are smaller, they will still mean your tank is almost completely fully stocked. If you go with a single male opaline gourami, however, you could put 6 of these small rainbows in as well. Nothing after that though.
Lastly, german blue rams have lots of blue on them but, again, it's a good idea to add some more tiger barbs to your tank first. Then stick to just one pair of the rams. You could keep one opaline gourami in with rams as well.
I'd also add a couple more cories, besides the extra tiger barbs and other fish, while you're at it.
I know its late now but the fish is actaully a Slender Mbuna very similar to a Johanni (Melanochromis johanni).
