Fleabitten greys are gorgeous! I have three
. The genetics are pretty interesting, but basically boil down to some horses which are heterozygous have a mutant gene which dies off as the horse ages and because the gene is deactivated, the underlying colour is allowed to show. The speed at which this occurs is different for every horse. I've seen a 16 year old Holsteiner who was probably 35-40% covered with fleabites. My own three fleabitten greys are 25, 37, and 30 years old, and are probably around 10% fleabitten.