That is interesting. Do you have any pictures?
My boy Shadow is a bay overo - sire was a black and white overo, dam was a dark bay (black) TB. He came out oviously bay, but he has silver points rather than black like a normal bay. Mane, tail and legs are all silver. I've always thought it was cool but never occured to me before to find out exactly what would cause that.
I wonder if they are similar.
It's no silver gene, I just found this: If the horse is bay (black only on the points), it will turn the legs some variety of brown or tan, and the mane/tail to cream (usually with black roots). These sometimes look like flaxen chestnut.
I don't trust wiki, but I found this conflicting... http://en.wikipedia.org/wiki/Silver_dapple_gene
Scroll down to first pic on the left. His legs are a little darker, but silver like that. Says nothing about mane and tail.
As for your baby, it says silver dilutes black, so I am very confused still. Hopefully someone will enlighten us.