Remember that Cirrhilabrus spp., like most Labrids, are protogynous sequential hermaphrodites, and that in the wild the male/female ratio is socially controlled. Terminal males are the result of sex changed females. These fishes are sometimes referred to as harmemic, but a more suitable description is that they are "lek" forming. Terminal males display not only to females, but to each other to establish their reproductive dominance, certain birds do this as well. Females swim at the outskirts of this lek and presumambly observe the males that have the most desirable traits, i.e. flashiest colors, to spawn with. Ideally to see these fish come alive with colors in the aquarium you would want a few females and at least two males. Since sex in these fish is socially controlled, keeping one small male by itself may cause that fish to revert back to female characteristics. I have seen this in many fish but particularlry Cirrhilabrus spp. and Genicanthus spp.. I am not sure why they do this, but female characteristcs may have less of a metabolic draw.
-BGreene