Black is more readily available. I pre-ordered the silver one a while back, but then Amazon emailed me saying it won't arrive til after Christmas, I canceled mine and grabbed the black one from Bestbuy. Now, Amazon still lists the silver one as not being released yet (only available from other sellers).
I don't think so. Amazon offered both when I ordered mine.
There does seem to be. I bought mine from Canadian retailer, Black's. The only silver one they had was the display model, which we took.