I have a GBR MF pair and the primary difference is in coloration, there are other distinctions as well. I imagine that these distinctions are displayed in all variations of the species. Look for longer first ray on the dorsal fin. It looks almost like the Little Rascals' Alfalfa hair sticking up, but in the front. My female does not have this. Her dorsal looks like it is relatively the same length throughout, tapering smoothly at the tail end.