Other Markings
Horses may have isolated body spots that are not large or numerous enough to qualify them as an Appaloosa, Pinto or Paint. Such markings are usually simply called "body spots," sometimes identified by location, i.e. "belly spot," "flank spot," etc. When this type of isolated spotting occurs, it is usually the action of the sabino gene.
Horses may develop white markings over areas where there was an injury to the animal, either to cover scar tissue from a cut or abrasion, or to reflect harm to the underlying skin or nerves. One common type of scarring that produces patches of white hairs are "saddle marks," which are round or oval marks on either side of the withers, produced by a pinching saddle that had been worn over a long period of time.
Read more about this topic: Horse Markings