A horse's coat colour where the basic colour of the body, mane and tail (which may be black, bay, chestnut or any other colour) is mixed with white hair. The proportion of white hair increases with age and sooner or later all grey horses turn completely white.

Young grey horses will differ in appearance depending on their basic colour; greying chestnuts may be called rose greys and greying blacks may be called steel greys. Some greys may go through a phase with a blotchy appearance (white blotches in a darker background), known as dappling. 

Some greys develop small darker spots (brown or black) which give them a speckeled appearance. These are known as fleabitten greys.