It is very difficult to tell when they are small and twice as hard when u are looking into a tank full of stressed out overstocked fish at the lfs.I have observed young dovii change color and patteren at will they can go from a solid horizontil line to spots in seconds. I think this type of identifying is better used on mature adults like around 8" + the only way i know how to sex most small juvinile cichlids is to observe their behavior like the tank boss will most likely be a male and the submisive ones that are not beat up are most likely female while the beaten ones are the lesser males.In your case already having purchased the fish time will tell if the fish is female it will lay eggs sooner or later and u will know then for sure but i agree with the others i say u have a lady.
and that's what monster fish do hahaha
