When I brought Pepee La Pew (sable ferret) to the vet last spring to inquire
about her underfur turning reddish brown, Dr. Lambourne told me that the
saliva can make the fur color become more red.  I think she mentioned it
happens in dogs.  This explanation makes sense to me: Pepee licks herself a
lot more than my other ferrets, even after having an adrenal gland removed.
The reddish color is also more pronounced on area easily reached by her
mouth: belly and sides.  Her underfur is still white on her head and top of
back.  All my ferrets are feed the same diet, only Pepee fur changed color.
Mind you, she is also my oldest.
 
The orange colored fur might not be due to the food. On the other hand, your
ferrets might have decide this color suits them better or it is appropriate
for Halloween ...
[Posted in FML issue 2108]