Dappling is caused by the red and black pigment in the hair of the horse. As this pigment fades and shifts with age and seasons, the dapples appear or vanish on the horse’s coat. Since dapples are a result of the shift in the pigment of the hair, trimming the coat can minimize the pattern’s appearance. This loss of pigment happens as a gray horse ages. Horses aren’t born with this dappled pattern. In fact, it appears after some time when the pigment starts running low. Only horses with the specific dappling gene get this pattern.