Bay horses do not typically have a true dorsal stripe. When they do, the color is called bay dun (or simply dun). Some bay horses, though, may have a black stripe down their back that is not a true dun stripe. This stripe is typically the result of countershading. In almost all cases, you can tell if the stripe is a true stripe or countershading by evaluating whether the horse has any other dun characteristics, whether the horse has a dun parent, whether the dun gene exists in the breed.