The coat of a bay horse can range from a pale brown to a bright orange brown to a very dark brown.  The legs are black from the knee or hock downwards (except for any white leg markings).  The eyes are brown.

Foals are brown when born with black mane and tail, and greyish brown legs.  The legs then lighten before moulting out to black as the foal reaches 4-6 months of age.

Bay horses are the result of a base colour of black combined with an agouti gene that controls the distribution of black pigment.

Bay is the most common colour in the horse.