He's a Frame Overo (also known as just "Frame," or just "Overo")
That's the jagged white spots.
I also go with the others on the splash white. The white on the face, the high white on his one leg and the white on his stomach that slips up, are all characteristics of splash white.
As for color he can't be a Dun unless you know that's in his genes. The "Dorsal stripe" could be countershading which a lot of horses have without having the dun gene.
I also believe he's a Sorrel paint.
People's opinions differ on the difference between sorrel and chestnut. Some think they are the same, others call one for Western horses and the other for English. Personally I believe if the mane and tail match the body color of the horse it's a Sorrel. If it's lighter it's a Chestnut.
Hope I could help!