I used to have a colony of M. estherae where both males and females are orange. Over time, the males get a slightly peachy color (and larger) while the females stay an intense orange.
They're a typical mbuna - a couple males and a few females make a nice colony. Crowding them helps decrease aggression. They like rocks (or pvc pipes) and hard, alkaline water....and lots of water changes and filtration. They appreciate a good amount of greens (spirulina flakes, algae, etc.) in their diet, although flakes and pellets are just fine.
They're mouthbrooders, so females hold the babies in their mouths for up to about about 4 weeks (depending on temps). Generally good parents. I raised lots and lots of babies from my colony...that the LFS was happy to give me a couple of bucks each for when they reached about 2".
Hope that helps! They're not rare, per se, but rarity doesn't a nice fish make