This mare is certainly stirring up discussions on a lot of the horse color forums, so I thought I would mention her here.
Normally I discount the designated breeds of the horses for sale on DreamHorse. Often what sellers do is list the breed the horse "most looks like", or perhaps whatever someone told them the horse was (or looked like). Sometimes I think it's just wishful thinking! But this seller has been very specific both on DreamHorse and on her own site that this horse is a registered purebred. It is even stated in the ad that the horse is "DNA typed, registered and confirmed purebred".
If you follow the link, you'll see that the horse is unmistakably a tobiano. (She is also a sabino, but that wouldn't make her unusual for an Arabian.) I think most people would agree that she's also unmistakably plain, especially for the pedigree that is claimed to belong to her. So it probably isn't surprising that many folks are calling foul, and that the registry has been contacted.
It may well be that somewhere along the line, papers were swapped and that mare is not really RWR Sonora. If so, the registry should catch the error when and if someone tries to register one of her foals. But if she does type out as Sonora (for whatever reason), then the truth is that tobiano will be in the purebred Arabian gene pool. To say that it would always be regarded with suspicion would be an understatement. But it would be there, and there would likely be enough breeders willing to take advantage to insure that it stayed there.
If I hear any more about the mare and her status, I'll pass it along.