Recent studies have examined the genetics behind white markings and have located certain genetic loci that influence their expression. On a gray horse, markings visible at birth may become hidden as the horse turns white with age, but markings can still be determined by trimming the horse's hair closely, then wetting down the coat to see where there is pink skin and black skin under the hair. Markings may appear to change slightly when a horse grows or sheds its winter coat, however this difference is simply a factor of hair coat length the underlying pattern does not change. Most markings have pink skin underneath most of the white hairs, though a few faint markings may occasionally have white hair with no underlying pink skin. Markings are present at birth and do not change over the course of the horse's life. Most horses have some markings, and they help to identify the horse as a unique individual. Markings on horses are usually distinctive white areas on an otherwise dark base coat color. All of these young stallions are chestnut, but unique markings can be used to identify individuals