First, this isn't a new issue. The color-temp change was done in 2.3.3. But alot of people skipped 2.3.3. Here's an article on AC that talked about it:
Google confirms Nexus S Android 2.3.3 update changed screen color temps | Android Central
Taking a picture of displays can be tough, as the white-balance setting of the camera itself can exaggerate the whole issue. But in that article, the phone on the right (supposedly with 2.3.3) looks better to me. The greys are way too purple in the phone on the left. Do a Google search for the 2.3.3 update and you'll find other pictures. Look for as many different pictures as you can to see if you can see a pattern. If you look at only one picture, you'll most likely find the real-world change is nothing like it.
As to what the 2.3.3/2.3.4 updates do: They set the NS display to a lower color temperature. In other words, the screen is closer to "standard" than before. However, most people, when viewing a properly calibrated screen, will think it's too warm; e.g. appear yellowish. But you end up with colors that are better represented and greys that are more neutral in appearance. Skin tones look more natural, too.
Now, I'm not saying Google is right and everyone just has to live with it. But, there are a lot of folks who like the new display settings, myself included. Some don't seem bothered, and others prefer it punchy and overly contrasty like before. In other words, we all have our preferences. So if Google were to "fix" this, it would really be best if they just make it a user adjustable setting.
Choice to the people!