Why is my rat's butt a yellow colour?

 
Why is my rat's butt a yellow colour?
I think it might be because his cage is dirty... he pees so much. :[
he seems fine except for the butt and he sleeps sitting for some reason recently. >_<
Help?
Probably the pee :D
Hope it's nothing serious

Source(s):

My Noggin(:
wipe its *** or wash it
it's because rat pee is so stinking strong. find some cleaner pets, eesh.