Halfbreeds were persecuted mixed-race Orions, crosses between the Green Orions, the Ruddy Orions and the Grey Orions.
Interbreeding between the subraces was feasible, but difficult; most had life-spans of only a few months. Ruddy–Green crosses were the most likely, given the numbers and health of each. Ruddy–Grey and Green–Grey were theoretically possible, but none were known to exist. The mutilated genetic code of the Greys meant that survival was highly unlikely—a hybrid birth would require intensive medical care, only found inside a guldin, a Grey Orion life-support chamber. A pregnant non-Grey would never be allowed out again.
Surviving halfbreeds had wildly varying traits from their parents, though all Green crosses had their distinctive body odor (and likely their pheromones too). They also received a strange mixed coloration of both of their parents, manifesting in spots or stripes like a zebra or tiger.
The mixing of the three subraces was not tolerated by the majority of the Orion population, and halfbreeds were thoroughly despised. Known mixed-race parents and halfbreeds could be attacked by furious mobs of Greens or shot down by Ruddy police or soldiers, and generally treated like vermin and hunted animals, not as Orions.
It was estimated that there were less than fifty or so halfbreeds scattered across the galaxy in the late 23rd century. A few mixed-race couples and their children could survive on non-Orion worlds, far from their culture and others of their kind. A few could potentially survive in the Orion Colonies, sheltered by sympathetic grandparents or by prominent families wishing to hide a scandalous affair, or by relatives needing a halfbreed as a patsy in a scheme. Discovery and death was a constant danger. (FASA RPG module: The Orions: Book of Deep Knowledge)