Yellow labs (Labidochromis caeruleus) are a species of mbuna from Lake Malawi, one of the Rift Lakes. You should read
this post to introduce yourself to the mbuna aquarium. It's a good starting point in your research.
This page contains profiles and pictures of many different mbuna species including those I'll list shortly...
As far as stocking goes, you'll quickly discover that mbuna are generally fairly aggressive, territorial fish. Your 30g tank (it's 36" long, right?) is the smallest tank I would consider keeping these fish in.
Fortunately, yellow labs are one of the few mbuna that would work in that small of a tank. I would go with a trio of yellow labs (1M:2F) and a similar ratio of one other species from this list:
Iodotropheus sprengerae (Rusty cichlid)
Psuedotropheus sp. Acei
Pseudotropheus socolofi
All other mbuna are likely to get too large or be too aggressive for a 3' long tank, but I think you'll find even this short list contains colorful, active, and interesting fish.
Hope that helps. Good luck!
