We've been hearing reports about 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:
"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 use