I don't know about the particular genetics, but I have seen many buckskins that have the "frosted" mane, in fact I've seen more buckskins with it than without it. I'm sure some of our color experts on these forums could explain the reasoning behind it, but I don't believe it's an uncommon thing in buckskins.
Here's a couple pics of my boy. He has blue specks in his eyes too, and they look gold, not brown. Again I guess because of the paint genetics... sorry the eye pic is blurry, but you can still see the odd color
I wish I could braid hers..if you even think about going within 4 inches of her ears she goes nuts. That's because she was abused...she's getting better though and she knows to let me touch them when I'm putting the bridle on.