Hello,
 
Ok, I don't know what causes yellow fur, but my silver girl and my
butterscotch boy both turned this icky yellowy-orange color right when
winter set in and now they're both shedding that fur and going back to
their "original" coloring.
 
As a biology major I would guess that it is similar to other animals that
change color for protection, etc.  In my experience the color change isn't
harmful in any way, just annoying to me since my pretty ferrets now look
stained and dirty.
 
Good luck, Cynthia
[Posted in FML issue 3707]