As far as I know, Billie is a varnish roan appaloosa. She's been roaning out over time. I didn't know her when she was a foal, but it would be interesting the contrast between then and now. These pictures are of her at about 8 and 12.
Granted, the first pic was taken in April and the 2nd in December, so the winter coat could be playing some effect, but primarily it's been a gradual thing over time. It's quite fascinating! I'll post a recent summer pic later.