Size
In general, Border Collies are medium-sized dogs without extreme physical characteristics. Males usually stand 19-22 inches at the withers, while females are a bit smaller at 18-21 inches.
Coat and Color
Border collies have a moderate amount of coat. Their double coats can be anywhere from slick to lush, and can come in many colors, although black and white is by far the most common. Black tricolor (black/tan/white), red and white, red tricolor (red/tan/white) also occur regularly, with other colors such as blue creme and yellow white, red merle, blue merle, "Australian red"/gold, and sable seen less frequently.
Eye color varies from deep brown to amber or blue with occasionally one eye of each color, usually seen with merles. The ears of the Border Collie are also highly variable — some have fully erect ears, some fully dropped, and others are semi-erect. Although working Border Collie handlers sometimes have superstitions about the appearance of their dogs, in general a dog's appearance is considered to be irrelevant. It is considered much more useful to identify a working Border Collie by its attitude and ability rather than by its looks.