Well, she is a horse that was born a Tobiano, but because she inherited the greying gene from one parent is now a white horse Yes, on horses that had colored hair, the skin there remains pigmented,in those former non white areas, and is visible when such a horse is washed
As many here know, my Appaloosa mare Charlie, were I to post a picture and ask to what breed of horse she was, no one, without knowing she was born chestnut, with blanket, high stockings and ablaze would, would recognize her as an Appaloosa, although, of course, those knowing the breed characteristics, would still see the mottled skin on her muzzle
Thus, the horse, depending on registry elligible for, would either be a pinto or a Paint, that unfortunately inherited the greying gene