Hopefully, someone with more experience will come along, but I have had 7 Itungi acei since last August. I haven't kept other acei variants, but based on what I've read, the Itungi behave similarly. The coloration of the sub-doms varies from light to dark black with yellow fins, while the most dominant often displays blue on his face and sometimes hints on his body when he's really showing off. The dominant also has a little more white in his dorsal fin. I keep them with msobos, hongi, and white labs, and the acei are very attention grabbing. They're definitely one of my favorites, and I would highly recommend them.
KL is correct, they are generally very docile. I've never seen any type of aggression from them against any other fish in my tank. And unlike all of my other mbuna they also seem to love to swim together higher in the open water column. When the males are displaying to the females, they are stunning IMO. They breed regularly(I have about 80 fry from them now) and are voracious eaters, hovering around the surface and sticking their heads out of the water when I feed them. You can literally hear the water snapping when they eat! The pictures in the link are from my original group, and here's one of their offspring from the last of a brood that I sold recently. He was stunning. Sorry about the poor quality of the picture, these guys don't stay still for a second!