I think (would need to double check) seal brown is just a brown horse, though there is another hypothetical gene (than regular brown causing it). Not sure on the technicalities. Either that or it's the same thing. I consider the first horse pictured seal brown and the others regular brown (see how much darker it is?) There is a horse in my barn too. Idk if that is just my definition though a "black" horse with some dark brown marks sometimes visible.
Brownskin = smokey brown.
black ( sorry Peppys!)
with cream. There is just some different terminology going on.