what is dominant white?
A.k.a  white spotting -  group of genetically related coat color conditions in the horse, best known for producing an all-white coat.
Dominant white
Dominant white or white spotting is a group of genetically related coat color conditions in the horse, best known for producing an all-white coat, but also able to produce various forms of white spotting and white markings, several of which are sometimes referred to as sabino.

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Dominant white [SEP] Introduction
In addition, different alleles which on their own give a white spotted but not completely white horse, such as "W5" and "W10", can combine to make a horse completely white. White can occur in any breed, and has been studied in many different breeds. Camarillo White Horses are characterized by their white coats.