Grey Horse w/ Long Mane

There are 4 tameable creatures with this look.

Grey Horse w/ Long Mane
Can Be Tamed
50Tiragarde Sound
Found in Winterdeep Basin and also south-west of Norwington Estate.
Can Be Tamed
50Rockskip Falls, Tiragarde Sound
Retains its original name after taming.
Freckles canters angrily about a small island in the river west of Norwington Estate.
Available to Horde Hunters Only
50Boralus & Hatherford, Tiragarde Sound
Friendly to Alliance. It can be found in the stable just south-east of Proudmoore Keep, and around Hatherord to the north of Boralus.
Can Be Tamed
50Tidebreak Summit, Stormsong Valley
Also found just north of the Deadwash.
* Level scaling: In Shadowlands most NPCs will scale with the Hunter's level, within the constraints of their level range. Hunters can tame regular NPCs up to 2 levels higher than them, but can only tame elite NPCs of the hunter's level or below.