JimmyC: If all 4S phones have the same 'warmer' white I'd be fine with that. But, I have two other iDevices as a yard stick, one that I still use very regularly, with a cooler, and to me, clearer white. I don't need to read the forums to doubt, I just look at my iPad.
I have quite a few iDevices too. Both my partner and I have had each iPhone, we both have iPads, and both got iPhone 4S's last week. The 4S's match each other and match the iPdid in colour temperature. I agree though, the iPhone 4 definitely had a blue-white screen, it was on both our iPhone 4's so accepted it, it was the first 'retina' screen so took it as one of its characteristics. But far from the warmer screen being faulty, I actually feel the opposite as it is much more natural.
Go to the Telecom store and ask for a replacement, but maybe comparing with other iPhone 4S's first would be better as I'm sure you'll find it isn't a fault with your iPhone as you'll probably find your replacement the same.