Buckskin is a bay gene overwritten with a single dilution gene. That's diluted bay, but you cannot be ever sure if the parents don't have any recessive chesnut gene which will appear as chesnut (no dilution), palomino (single diluted chesnut) or cremello (double diluted chesnut).
But the stallion of quality usually have their gene map about colours, you can see it in the description like this ("Aa ee crcr gg"). Do not breed with stallion with "ee" (they are chesnut, palomino or cremello), possibly not with "Ee". Breed with "EE". They don't have any chesnut gene.
Buckskin (EE)×buckskin(EE) = 50% buckskin, 25% perlino, 25% bay.
Buckskin (EE)×Bay (EE) = 50% buckskin, 50% bay
Buckskin (EE)×Perlino (EE) = 50% buckskin, 50% perlino
Bay (EE) × Perlino (EE) = 100% buckskin.
Mares usually don't have such gene map, but tehir colour genes can be tracked if you look the parents of the mare and the foals she had before.
As you can see, the latest version is the best if you know or at least guess what colour genes the mare has.