I'm betting that's from a Barred male over some other colored female with dark legs. Rocks should have yellow legs. They will often have a dark 'wash' over their legs, but their actual legs should be yellow, and the wash will mostly be on the front sides and down the toes.
If that's from a hatchery and not an SOP breeder, that's probably a male. Give it a couple weeks and the legs will probably yellow up. Give us another whole body picture in a couple weeks and we can tell you for sure.