How do I differentiate between ground and neutral in black-white-red wiring?
Can you trace the cable back to the service panel or to another outlet (if there is another one on that circuit) and do a visual inspection of the wires?

Failing that, you could temporarily wire in a GFCI, guessing at which wire should be neutral and which ground.  Plug in an appliance, turn it on, and if the GFCI trips, you got ground and neutral the wrong way around.