i would say behind that teddy bear coat he is wearing would be a nice mousy dun as his mane is dark and body a little lighter hard to tell with a huge fluffy coat but thats my opinion
The colour is variously known as blue dun, grey dun, mouse dun, silver dun, grulla, grullo - along with probably a few other shades / names I've missed.
In technical genetic terms, it is a black pony with dun overlaying it.
The proper term would be grulla, but I do tend to call it either black dun (describes exactly what it genetically is) or blue dun (because it does tend to have that slate blue colour when in summer coat - in winter goes a very odd colour indeed!
I currently have four of them, and am praying my imminent foal will make five!