Definitive way to sex Bolivians?

[Breakthecycle2]

I had what i thought was a pair, but now I realize they might be males. The black front part of the dorsal fin on both are higher and the bothe of their bellies are yellow.

 

[Ben]

IME, males have much brighter, sometimes darker, colours and the end of the females dorsal fin is rounded while the males is pointed.
Forgot to add, Males can get a tiny bit larger where as females get plumper
DD