There are two basic ways horses turn white, or "grey" as hair does when it ages.

One is a rapid whitening of both body color and points between birth and age approximately age five (more common to Arabians, and others.)

The second retains dark points and dark body color much longer, reaching the dappled grey stage at age 8 or 9, and going white in their teens (more common to Percherons, and others.)

All Grey horses like this Arabian foal and his mother are born colored, and whiten over time.

These photos show horses quickly-greying horses, going through the dappled stage and turning white before age five.

This 17-year old Spanish Arabian is a Flea-bitten Grey and has many small red (and a few black) spots. On the inside of his left foreleg, he has a large red area called a "bloodmark" which increases with age.

The slower-greying type has a much longer period of time with a grey face, darker body, dark dapples (around age 8 or 9 years of age), and darker mane, tail and legs into late adulthood. (Horses in this phase are sometimes mistaken for Blue Roans, but roans always have darker heads and faces, not the opposite.)

Slowly-greying horses in their teens with varying amount of black on legs, mane and tail. (All of them have at least dark knees. )