Nexus S' Android 2.3.3 update adding a yellow tint to the screen and even washing out its colors, but according to Google's Ry Guy, said patch is indeed intended to tweak the display's color temperature. Here's the full quote from Google's support forum:
So while this display tweak is well-intentioned, it looks like many commenters on both the forum and XDA-Developers aren't too happy with this. Being curious geeks that we are, we went ahead and manually updated our own Nexus S (and by the way, be sure to match your build number with the appropriate patch). As you can see in our comparison photos (shot with the same manual camera settings and medium screen brightness), the new overall color temperature is no doubt subtly warmer, although the dimmer brightness settings no longer suffer from the aforementioned red tone. Interestingly, we actually approve this change, and the Super AMOLED display certainly doesn't look washed out to us, nor do we see any noisy dithering that some have reported. Surely we can't be alone. Well, there's only one way to help solve this mystery: if you happen to be a fellow Nexus S owner who's applied this update, why not chime in below?"With your new OTA complete, you may notice a slight difference in the way colors are displayed on your Nexus S. For Nexus S, we have adjusted the color temperature settings to more accurately reflect darker colors at all brightness levels. The Gingerbread UI being darker, we found that the colors were not as accurate when the device was being used at lower brightness levels. For example, some users reported that the initial color temperature was too high leading to some darker greys having a reddish tone; with the new color temperature this is no longer the case."
[Thanks to everyone who sent this in]