The problem with line bred for color cichlids, is that many of the normal sexual differences (such as spots in certain areas,, or melanin) are bred out.
In normal dovii its pretty easy, but with these, at least until a couple naturally pair up, only venting is reliable.
To tell you the truth, I find it even difficult to determine species. If you hadn't said dovii, (to me) it could be any number of generic central american cichlids.