Hi Rob...long time no see!!
Blue Acara... the males anal fin is wider than that of the females. The males dorsal fin is also longer and pointed, whereas the females is more rounded. I think it's difficult if they are juvies though Rob
In my own experience, it's the males that are more colourful but obviously my cichlids are african not central/south american so that might not necessarily be true. I will have a google & see if I can find any male/female pics