Bay is a dominant colour and it's different shades are common and very prevalent in most breeds of horses. There are many different terms used when describing the different shades of Bay. The most popular being Bright Bay, Mahogany Bay and Light Bay. Regardless of the terms used to classify a shade of Bay, all Bay horses will have a red body, ranging from light to dark. Bay horses always have black points - legs, muzzle, mane and tail, and the tips of their ears are black. Many Bay horses will have white markings that cover the black legs. Bay is a Black horse genetically altered - this alteration is brought about by the dominant form of Agouti which will limit the distribution of black hairs to the points of the horse, thus creating a Bay horse. 

"Wild" Bay is considered a subtype of Bay. A characteristic of this subtype is that the black on the leg will only extend up to the pastern or fetlock. When it reaches the cannon it fades out leaving a mix of red and black. This subtype of Bay is considered fairly rare. As Bay is also the base for colours such as Buckskin or Bay Dun, this same restriction of black on the legs happens in other Bay based colours also. It should be noted however that this is different than the legs of Bay foals who have not yet shed their foal coat. Upon shedding the foal coat the legs will be black up to the knees and hocks. The colour of a foal is not really accurate until it is a yearling in it's natural length summer coat.

A Bay horse put to a Bay, Black or Chestnut horse could have a foal which is either Bay, Black or Chestnut - each pairing is capable of producing all three possibilities.

Bay based colors include:
• Bay diluted by Dun is called Bay Dun or (mostly outside the UK) Zebra Dun
• Bay diluted by Cream is called Buckskin when there is one copy of the cream gene and Perlino when there are two copies of the cream gene - Perlino is the only modified version of Bay that has a different appearance in single (Heterozygous) or double (Homozygous) doses.
• Bay diluted by Silver is called Silver Bay, Bay Silver or Red Silver
• Bay diluted by Champagne is called Amber Champagne
• Bay altered by Roan is called Bay Roan or Red Roan