Bay (A) is one of the foundation colors. Ponies are either black, chestnut, or bay/brown with some ponies having other colors diluting/modifying the base colors. Extension and agouti form the basis of all equine color. Extension determines whether or not a pony has black or not and agouti determines where it will go. Bays have the dominant form of agouti and the dominant form of extension. Agouti restricts black to a bay's points while the rest of the body is a shade of tan. There is a test available for bay.
The shades of bay can go from near black to red to light sandy brown, but all have black manes and tails and black legs. Bay foals will not have black legs until they shed the foal coat. Manes, tails, and bay foal coats can bleach in the sun.
Wild Bay, or low point bay, are bays where the black points are even more restricted than on regular bays. The black legs are noticeably shorter or are barely present. The body color is often light bay. It has been found to not be genetic.
Bay is likely an original color in Chincoteagues as it is widespread and the breed was originally all solid dark colors. A 1891 article in the New York City newspaper The Sun stated that the ponies "are most frequently black, gray, sorrel, or dun (buckskin)." Leonard D. Sale wrote in 1896 in The Horse Review of Chicago that, "The prevailing colors are bay, brown, chestnut and light sorrel. A Washington Post article from 1902 stated that the prevailing colors were bay and black. A 1923 St. Petersburg Times article described the ponies as "bay, gray, dun (buckskin), black, and sorrel". A Delmarva Star article describing the 1930 Pony Penning described the ponies as "many colored", with blacks, browns, bright bays, and so many with spotted coats."