Flaxen is a coat trait that causes the mane and tail of chestnut horses to be noticeably lighter than the body coat color, often appearing golden, cream, or blonde. The degree of expression varies considerably: some chestnut horses show only slightly lighter mane and tail, while in others the contrast can be very pronounced. Flaxen should not be confused with the silver dilution caused by the Silver (PMEL) gene. Silver gene is not present in the Thoroughbred breed and while both can produce lighter manes and tails, the silver gene affects black pigment and therefore alters black and bay coats, whereas flaxen appears only on chestnut horses and does not dilute the body coat itself. The inheritance of flaxen is not fully understood. Earlier studies suggested that it might be caused by a recessive allele, sometimes described as "Ff". More recent observations, however, indicate that the trait may be polygenic and influenced by multiple genes. There are documented cases of flaxen chestnut foals born to parents that are black or bay, suggesting that the genetic factors responsible for flaxen can be carried without being expressed and may be masked in darker-colored horses while still being passed on to their offspring.