According to Weatherbys, the company that administers British racing under contract to the British Horseracing Authority (BHA), the main body colours found in thoroughbred racehorses are bay, black, brown, chestnut and grey.
Bay can cover many variations of the colour brown, although typically means reddish-brown, or tan. A bay horse has a black mane and tail and a distinguishable colour line between the upper and lower sections of the legs. By contrast, a brown horse has a brown man and tail and no such colour line, although tan may be seen in the fold of the flank and/or muzzle. Purely black horses are a rarity and must be entirely black, in coat, stifle fold and muzzle, to be classified as such. Chestnut horses have a reddish or yellowish brown body colour, with a mane and tail which, while similar in shade, may be slightly lighter or darker.
Grey, too, covers a range of shades from bright white to battleship, or gunmetal, grey. Grey horses are not usually born grey, but grow lighter in colour with age, such that their body coat is a mixture of black and white hairs. Truly white horses, like truly black horses, are a rarity.
In addition to the basic body colours, certain other colours are recognised by thoroughbred and non-thoroughbred authorities. A thoroughbred described as ‘roan’, for example, is characterised by white hairs evenly intermingled with hairs of another colour, such as brown or chestnut. That said, most thoroughbreds that appear roan are in the process of going grey.