I compared the two and the 3GS looked a tiny bit more blue, not yellow.
These same threads happened last year and Apple patched it.
That was a color temperature difference. If you would have read the thread, you would have seen that I held my 3G S up to a friend's and his was nearly as white as my old 3G.
There is a problem here, even the Apple support rep agreed with me.
My 3G S was ordered on the 9th and shipped out of Memphis, TN. My friend's (which looks fine) was ordered on the 10th and shipped direct from China.