Personally, a Mayan looks like that 10 year old shirt you can't throw away... faded and washed out. While Festae look like that shirt did when it was brand new. I'm gonna grow these out, idk if the one will make it, it's been pretty beat up. But the one is doing well. If it looks like it could look decent I'll grow it out a bit more and trade it off for something. Depending on it's personality, I may just keep it, unless it tries to kill any of my other fish then it's gone.
Male festae have been known to have black in their dorsals, so at the size it is, thatd be as reliable as a coin toss and upwards of 6-7 inches, still wouldn't be 100% reliable.
In Uros, both males and females have black in their dorsals. They are identical looking in almost every distinguishable feature. The only way to tell is by venting.