Depending on the subspecies....male blue devils will get an orange or red stripe on the end of their blue tail....females remain all blue with clear fins. Male fiji blue devils will get an orange or yellow belly/throat region with yellow or orange on their tail fin too...females remain blue but some individuals may show a light dusting of these colors. Oh, and these markings will only show up as the male matures...not sure on how to tell their --- before hand!
HTH :yes: