I've had Black Bar Endlers for several years and don't cull or intentionally breed them, just give them away when I get too many. There are a couple like this, is this normal or some kind of inbreeding? I believe this is a male, with a female body shape and some male coloration.
Hmmm...that looks like the gravid spot that females have. I can't remember the term off the top of my head but try looking into the following:
Early developing males vs late developing males. I know this happens in livebearers. Early developing males are smaller, but can pass their genes on quicker. Late developing males are the flashier, larger fish, but have to wait a while to pass their genes on.
"Impostor" males? I can't recall if this is a thing or not in livebearers, but I know it's a thing in wrasse.
It could also just be a very dull colored male. They don't have to be super duper colorful...although that certainly helps in attracting a mate...and a hobbyist.
"Many livebearers are known to have coercive mating strategies, where males don’t court but rely on forced copulations with uncooperative females. Mimicking females might allow such males to trick unsuspecting mating partners. Clearly further research is required for us to better understand the role of anal spots, both in females and in males. "
The selective pressures in tank life are different than the natural environment which forced the amazing amount of dimorphism in the species ... so maybe. I remember reading a scientific publication called something along the lines of "sneaky f-ers" about non-dominant male deer that evolved to be sneaky, to wait until the dominant males were fighting over the female to then go and "make their play" while the other males were busy with the fight. Nature finds a way.