Not sure about the fin. My female has orange stomach blotch, and slight orange/yellow coloring to upper fins. My male has a blue black coloring. No hints of red or orange at all. He's under an inch, and she's under half an inch, so I can't really answer my question. Mine are quite obviously a pair (Though young, and apparently not quite mature yet).
Without the stomach blotch of orange, I would say he's a male.