I remember reading somewhere when I was in the process of researching my T2i purchase that people were having problems with color temperature shift as the camera heated up (after about 20 minutes of recording, I think).
I also remember that some of the solutions were to disable the LCD display once focus was achieved, and of course to install Magic Lantern to give you more control of white balance and color temperature.
Joe Bourke
Owner/Creative Director
Bourke Media
http://www.bourkemedia.com