It could be light getting in through the veiwfinder. On certain cameras it is possible to blank off the eyepiece. This would be particularly noticable in both strong and weak light when using tripod or not actually putting your eye against the veiwfinder when taking the photo.
Alternatively, there may be a way of adjusting the "white balance" for extreme exposures. This often consists of pointing the camera at a known white surface so that it fills the frame and pressing a button so the camera can adjust to the lighting conditions.