Here's why:
* Blood bay: A blood bay horse has a rich, reddish-brown body color with a black mane and tail.
* Sooty: Sooty is a modifier that describes a horse with a darker, more "dusty" or "smoky" coat color. The black hairs are more prevalent, giving a darker appearance.
Therefore, a horse that exhibits the characteristics of both blood bay and sooty would be a sooty bay.