My gameworld doesn't have half-orcs, but does have full orcs as a PC race (just using half-orc stats). This document makes them a base race with several subraces.
Bestial Orc - brown-skinned, large, tough, and easily angered
Demonspawn Orc - half-orc, half-demon, hairless red orcs that can be scary
Forest Orc - green-skinned orcs that live in and respect the forests
Grey Orc - the most common orcs (your basic half-orc from the PHB)
Snow Orc - white orcs that like the cold