sexual dimorphism regardless of skin chosen
please add either a model/sound/skin/animation difference for us to be able to tell male from female.
I would highly suggest a sound or animation added to make it easier for males and females to tell each other apart even from a distance. For instance the male broadcast could sound deeper and from up close the male could greet another of his species with a specific animation that will make it clear he is male, likewise the female broadcast would sound sharper and she would also get her own animation to show she is female to others of her species.
As i see it, doing it this way would grant you the easier job of not having to change every model nor have to alter any skins.
regardless though of how you choose to do it i know for certain that realism servers are definitely going to appreciate it if you add something like this into the game to make identifying males from females easier for each species. :)