I have read a great book on horse color genetics, and of course brindle is one of the things talked about. To quote the book, who's quoting someone who's done extensive research into brindle horses, "Brindle horses have texturing in their coat, similar to that seen in some Appaloosa horses. The pattern seems to be inheritable especially in terms of coat texturing, but the extent of striping is highly variable" I liken it to what I feel when I'm grooming a clients paint horse. She doesn't have rain scald or anything, has been thoroughly looked over by a vet, but her white sections feel raised up higher than the colored sections of her coat, the coat feels the same softness, but just a bit of a bump up going from the colored to the white sections. It does say that some people mistake extensive dun markings for brindling, and that some horses are born with ghost markings (dun like, as well as brindle), but as they lose their foal coat, those markings disappear.