Sorry what I meant by chestnut's taking genes away is that they can hide so much if the black gene doesn't carry on. Pretty much only cream and dun are the only dilutions that actually show up on them. So unless the dun carries on the black gene the chestnut is 'taking away' the other genes, by hiding them. Sorry for the choice of words.
Cool to know about the silver gene in stocks, I didn't take breed into consideration, thanks.
Yes, black and grullo are possible but I doubt it, most chestnuts carry at least one agouti gene, and him being a bay dun leads me to believe he does too - so while it's possible, I doubt it'll happen.
I think chestnut, bay, bay dun and chestnut dun are the most likely outcomes. With black and grullo being very rarely likely.