He was one of the Greats...

[Nanno]

With rare exception, all gray/white horses, regardless of breed, start out a dark color. Usually they fade dramatically in the first two years and are quite obviously gray by the time they're three. Jet took his time and stayed black until he was four and was a dark steel gray when he was five and six before he turned dapple. He stayed dapple gray for quite a few years before turning fleabitten gray last year. 

But as to his breeding, Jet was a Quarter Horse/Trakehner cross. I had the opportunity to breed my old style bulldog Quarter Horse mare to a son of Abdullah when I was a college. Jet was the result of that union.