If you're familiar with genetics, en.wikipedia.org/wiki/Hor...r_genetics is a good place to start to learn.

The "problem" with a grey dam is that daddy can be almost anything, as long as he carries the genes for your mare.

The things he CAN'T be are perlino, cremello, and homozygous tobiano. Tobiano has the same way of working as grey, so a homozygous tobiano will ALWAYS pass on one tobiano allele, making the horse a tobiano (a heterozygous tobiano will only create 50% tobiano foals).

Perlino and cremello would pass on one cream dilution allele, making your horse a dunskin. Since she's a dun, we can rule that out. However, daddy could be a palomino or a buckskin, since he might not necessarily pass the dilution allele on.

The other thing is that with your mare, the genes that control her color are mostly dominant (dun and base coat color). So from that, you can know that at least one of her parents was dun. However, that could be the mare, and the dun was covered by grey. At least one of her parents had a black base color (black, bay, buckskin, etc.) rather than a red (chestnut, palomino, etc.). Possible combinations would be bay x red dun, buckskin x grulla, chestnut x dun.... the list goes on and on, unfortunately.

If that doesn't make sense, I can explain it further, but I'm still waking up...