Horde hunters can tame this horse the usual way, but it is friendly to Alliance and can only be tamed by Alliance hunters using the toy "N'lyeth, Sliver of N'Zoth" while in War Mode. It can be found in the stable just south-east of Proudmoore Keep, east of Proudmoore Keep by a cart, and in stables by the wall between Ashvane Docks and Boralus Harbor.
Horde hunters can tame this Workhorse the usual way, but it is friendly to Alliance and can only be tamed by Alliance hunters using the toy "N'lyeth, Sliver of N'Zoth" while in War Mode. Found just across the bridge, to the east of Vigil Hill island. Only one is present at a time, but if the current one isn't the colour you're after you can kill it and it respawns quickly.
Level scaling: 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.