Wow! I love this color, especially on a black horse. *swoons*
It looks to me like this horse is just a very loud sabino. There could be some kind of dominant white or something in there that is making it so extensive.
Is it just me, or does this color seem to be a consistent phenotype of some kind? When I see a horse of this color, after I wake up from fainting (haha), I notice that it looks almost exactly like the others I've seen. I wonder if it's caused by a specific variation of sabino or something.
@walnutpixie As soon as I saw him in the pasture I made a b-line to him, totally passing up my horse, haha. I love his colour. I've never seen a sabino quite like this, especially gray, so that's what's throwing me off.
@sorrelhorse the only white that crosses his back is that one spot by his withers.
Walnut the phenotype is very typical of the same sabino or dominant white that is in Clydesdales. I think it is dominant white, it just has that flaky look to it. Here is a TB filly, she is slightly more extensive than the horse in the OP, but you can see the similarities:
I think the horse in the OP is black, and not going grey. Dominant white is a mutation of the KIT allele, which is also where tobiano and sabino are, as well as roan. If you think about the phenotypes of those three, you get a lot of roan effects from them, which I think is the case of this horse. Similar to the colouring of a Clydey, like this one:
As far as what you would call it, I would call it what it appears to be - dominant white. As far as what the horse would be registered as, well that depends on the body. As far as I know, no body has dominant white as an option as yet, so they would all be wrong.
Does the white cross his back anywhere but the neck?
I see a grey sabino and tovero if it crosses the back, overo/sabino if it doesn't.
Tovero isn't a single pattern. It's what the APHA calls tobiano with sabino, frame, or splash. It's a very misleading word and needs to be taken out of horse owners' vocabulary because, by the APHA's own standards, any "tobiano" with any sort of white on its face should be registered as a "tovero." It's misleading because frame is the only gene that's lethal in any way and it is only potentially lethal when crossing two frame carriers.
Back on topic: I'm awful with dominant white. I thought sabino before I scrolled down to see the entire picture, but after seeing the whole horse, I thought DW, as it seems to look more along the lines of the DW horses I've seen.
Walnut the phenotype is very typical of the same sabino or dominant white that is in Clydesdales. I think it is dominant white, it just has that flaky look to it.
Oh, neat! I was thinking that it was something like the pattern on Clydes. I think I've heard it be called Blagdon or something liked that on heavy horses. Interesting that it would likely be dominant white. I guess that means I was on the right track thinking there was a gene that caused this coloring specifically.