It would almost definetely be a chestnut but an extreme anomaly can occur and the horse could even turn out to be dun under conditions of about 50'000 to 1
Whatever colour either of the parents are the foal could be, and it could just be any random colour, but the most common is the colour of either of the parents.
A buckskin horse carries three important colour genes: the black gene, the agouti gene (which restricts the colour to the points, creating bay) and one dilution gene (changing bay to buckskin).
If...
It would simply be a paint/ mustang cross. There's no special name for it that I know of.Well I am answering this about howrse.com the answer depends on the genetics of your mare. If you mare is 50...