One genus of dwarf cichlid that seems to get little attention yet includes, in my opinion, some of the most colorful species is Congochromis. These small cichlids (~ 3″) are found in shallow streams within the central African continent (Gabon, DRC, and Central African Republic).
Most of the information available online for this genus focuses on only a couple of species, which you can easily find with a Google search. However, one of the most comprehensive profiles of C. sabinae that I found is on the Seriously Fish website. Fishipedia.fr has some additional nice photos of C. dimidiatus and C. sabinae. As Ted Judy pointed out in the January/February 2017 edition of Tropical Fish Hobbyist, C. dimidiatus would make a good choice for a cichlid nano tank. Unfortunately and I’m not entirely sure why, but none of the species in the genus seem to be easily found in the hobby.