In general, Border Collies are medium-sized dogs with a moderate amount of coat, which is most often thick and sheds often. They have a double coat that varies from smooth to rough and is occasionally curled. Whilst black and white is most commonly seen colour pattern of the Border Collie, the breed appears in just about any colour and pattern known to occur in dogs. Some of these include black tricolour (black/tan/white), liver and white, and red tricolour (red/tan/white) have also been seen regularly, with other colours such as blue, lilac, red merle, blue merle, brindle, and Australian red (also known as ee red, blonde, recessive red, or gold) which is seen less frequently. Some Border Collies may also have single-colour coats.
Eye colour varies from brown to blue, and occasionally eyes of differing colour occur; this is usually seen with merles. The ears of the Border Collie are also variable — some have fully erect ears, some fully dropped ears, and others semi-erect ears (similar to those of the rough Collie). Although working Border Collie handlers sometimes have superstitions about the appearance of their dogs (handlers may avoid mostly white dogs due to the unfounded idea that sheep will not respect a white or almost all white dog),[3] in general a dog's appearance is considered by the American Border Collie Association to be irrelevant.[4] It is considered much more useful to identify a working Border Collie by its attitude and ability than by its looks.
Dogs bred for show are more homogeneous in appearance than working Border Collies since to win in conformation showing they must conform closely to breed club standards that are specific on many points of the structure, coat, and colour. Kennel clubs specify, for example, that the Border Collie must have a "keen and intelligent" expression, and that the preferred eye colour is dark brown. In deference to the dog's working origin, scars and broken teeth received in the line of duty are not to be counted against a Border Collie in the show ring. The males' height from withers comes from 48 to 56 centimeters (19 to 22 in), females from 46 to 53 centimeters (18 to 21 in).