I remember the thread from a while back.
It specifically mentioned some BP's that had changed color after a regurge. It was even suggested that the rat's themselves may have been the cause, something about the rats being overly fatty?
I've seen many many photos here of balls that mysteriously changed color, some literally in a single shed, but so far as I know, it's never been proven anything other than one of the many mysteries that are Ball Pythons.
Gale