The "warmer screen" is not even yellow on my new iPhone. Certainly, there could be defects that resulted in a DEFECTIVE yellow tint. However, this is definitely not the case, mine is just warmer, never leaning towards an overall yellow stained screen. Although some people can mix these 2 things up.
Certainly there's a difference, I can admit to that. However, by no way is one screen type superior than the other. It's all personal opinions and how your perception of a "correct" screen is. Blue has nicer blues and warmer has nicer yellows.
If it really bothers you that much to have a warmer screen, simply return it and wait for the next iPhone, it would be more of a hassle to go through a few and still not get what you want (which seems to be the current trend). 😛