white rat fur color change on head and neck

Question
I have two female rats a few months old. I returned from a vacation and noticed my white rat's head and neck looked browner.  The other rat is brown and seemed to be grooming her when I noticed it.  She's acting normally, eating OK. Should I be worried?

Answer
She has porphyrin staining on her fur.  Porphyrin is the red discharge that is often seen around the rats eyes or nose and there tends to be more of it during times of stress from illness or other situations that causes the rat to be upset etc....   When they groom themselves, they wipe their face with their front paws and if they have the porphyrin discharge, they will smear it onto their fur, staining the fur a brownish to brownish red color. Its also noticeable on their front paws too.   It will wash off easily. She may have been upset you were not around which made her produce more porphyrin discharge.