I noticed this same sort of shift in color on my GL2 mainly in the whites also (mostly changing from a white to a yellow-ish white to a blue-ish white). I noticed it during a test of the interval record feature so footage was separated by time (I believe it was every 30 seconds capture 1 second of tape). I do not, however, remember if I was in auto white balance or not, but I have seen this same thing happen in my GL2.