As far as I know, harlequins are an unproven trait. They just appear.

I wouldn't mind having a nice looking female, like Becky's. But I wouldn't attempt to breed a male because as far as I know, they are normal.

I remember at a show a couple years back I saw a harlequin running at $500 and the guy admitted he didn't know the genetics behind them. Just thought they were funky normals.