If you really, really want to be sure about the color, there are laboratories that can tell you - for a price. 

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I was only speaking black. No dilution gene. Yes, you could get a buckskin with a smoky black though.Actually, you CAN sometimes get a buckskin from a black/chestnut pairing.
You need black (from the black parent).
Plus agouti to make it bay (would have to come from the chestnut parent, who can have it without showing it)
Plus the cream gene (can be carried by the black without showing it--"smoky black")
So possible, but depends on each parent having a particular gene that you can't tell by looking at them.
I don't know what color the foal is, just talking about the genetics here![]()
It's only about 25, and can be a very useful toolIf you really, really want to be sure about the color, there are laboratories that can tell you - for a price.![]()