Horses (and dogs) can also get this. It may or may not affect the hair (resulting in white patterns). Reticulated leukotrichia is a form that is found in Thoroughbreds and Quarter Horses and Standardbreds with Thoroughbred ancestry, which forms a broken or wavy line of white hair down the spine. It's also common in Arabians.
The fading may come and go with areas losing pigmentation and then regaining it. It's purely cosmetic and doesn't affect the horse's health.