Some indicators I have observed regarding gender differences among males which have not yet developed blue facial pigmentation and females of similar size:
One indicator is dark pigmentation among the pelvic and anal fins. These fins remain distinctly yellowish among the females. The fins of the juvenile males are darker. This dimorphic characteristic occurs before the facial change does and is evident when the male is in the 3"-4" size range.
Another indicator is the shape of the anal fin. The end of the female's anal fin is rounded while that of the male is tapered. The dorsal fin tips are similarly shaped. There is also greater distance between the end of the female's anal fin and start of her caudal fin. The distance between the two fins is shorter among males (the male's anal fin tip will significantly extend pass the base of the tail base among fully matured specimens).
Juvenile females possess more yellow coloration around the throat and gill plates than juvenile males. This is evident when the fish are in the 2.5"-3" size range.
Female (left), male (right, displaying the above signs of dimorphism)