There is a interesting bug in iPhone 4 photos where a blue tint shows up in the middle of the image. This bug has been widely noted and appears to effect only the back, 5mp camera and not the forward facing VGA camera. It also seems to still be a problem under iOS 4.2.1. Some have stated that this may because of the lighting conditions, while others have noted this effect under many different types of light.
I have not had this issue myself with my iPhone 4 or heard of any of my friends having it either. I wrote too soon! I tried taking a picture of a white blanket with my iPhone 4 for the post... and here is what happened..