Hmmm let's see, I'm not an "expert" but the sooty buckskin carries a creme gene on "bay". (which is black with 'agouti")
The black mare could possibly carry a red gene recessively. So the best i can tell you is that you could get,
buckskin, bay, black, smoky black, or possibly sorrel (if both carry a red gene recessively), black is dominant so black shows and hides red if the horse has one red and one black.
or palomino with the stallion's creme gene and a red gene from both parents?
Someone else may be able to explain it better and they could correct me if I'm wrong.
And WELCOME!
Anne