This is known as a flea-bitten gray horse. A roan pattern, or “varnish” shows up as white hairs appearing through the base coat color of the horse. Roan horses are born with this coloring.

According to Horse Racing Sense, roan is the mixing of white hair with a horse’s base hair color, which lightens as the horse gets older. A gray foal can be born chestnut, bay, brown or black ...