Bay was probably the first mutation from the Lineback Dun coloration of the wild horse, the absence of the interference pattern which produced its camouflage coloration. Today, the majority of horses in breeds not selected specifically on coloration are bay. This may once again have been due to the fact that bay horses, possibly occurring naturally in wild herds, were easier to single-out for initial capture; or possibly because, being novel, they were less likely to be eaten after capture. The horse pictured at the top of this page is a bay of the most typical shade. The glow of a Bay may be either reddish (as the photo above left) or golden, depending upon the actual shade of the horse.

Depending upon the amount of Sooty, Bays can either be clear bay or nearly black.

A deep shade to the red hairs on a bay results in a Blood Bay.