I got my white back plate in yesterday from
http://applepartsstore.com/index.php/ that was posted earlier. I've always wanted to try the black front/white back since I first saw someone do it after the 4 came out.
I ordered the 4S white back plate for $25 and free shipping, and it's the real deal. They state on the website that it's OEM and I have no reason to believe otherwise. It's EXACTLY like the black OEM back plate. The shipping was fast and I can't recommend this website enough if you need OEM parts.
Of course, I also had to order a pentalobe screwdriver, but I didn't want to pay $15 from them for it, so I bought a cheapie off eBay. Wouldn't you know it? The darn thing is just a bit too big for the pentalobe screws on there!!! So, here I sit with my new back plate and bumper, but no way to install it. Dang!
I'd like to get this thing on there this weekend, so can someone suggest where I should look locally for a pentalobe screwdriver? I would assume a hardware store wouldn't have something like that, but maybe a eyeglass store or Radio Shack? I'm dying to get it installed!