Cobalt Blue Zebra (Metriaclima callainos).
Members of the zebra complex (metriclima/maylandia genus) have a more 'stocky' build than the 'torpedo-shaped' pseudotropheus socolofi's. Cobalts also lack the black fin markings and have a different head and mouth structure.
As for gender, I'm leading toward female based on:
-the proportional size of the pelvic fins (the same fins of matured males would be longer)
-rounded dorsal and anal fin tips (fin tips of the males are tapered)
- overall color of the fish (more gray-blue than the vibrant blue that the males display).
With all that said, an immature male could potentially possess fin characteristics and coloration of the opposite gender, so venting (visual inspection of the fish's openings) is recommended for absolute gender confirmation.