Probably the best indicator for female in RT, once the fish is past the very young juvie stage, is the dark/black coloration of the first part of the dorsal fin. Never seen or heard of a male RT that pocesses this trait.
The fish in question apears to have the first part of the dorsal fin black, but the first part of the dorsal fin in the picture is down so, actually, you really can't tell for sure. Otherwise the fish has traits more typical of a male: yellow coloration, blue spangling, green on the face, and longer finnage.