Michele,
What color are the ferrets in question?  There may be a simple explanation.
Is it possible that they are going through a coat change?
 
I encountered something similar many years ago after one of my girls
(chocolate) was spayed.  About 1 week after her surgery I noticed that she
looked bruised around the incision.  It concerned me at first because it
didn't make sense for there to be any bruising that long after the surgery.
Bruising, if it happens at all, usually shows up within the first 24-48
hours I've since learned.  When I looked closely I realized that it was just
new hair growing in and it was giving the skin a bluish, bruised appearance.
 
I've encountered this "phenomenon" many more times in the 7+ years I've
owned ferrets and anytime I get a call from a concerned owner I always ask
if the ferret is going through a coat change.  It always turns out that
that's exactly what's going on.  Obviously, this is not something you would
see in a white or very light colored ferret.
 
Hope this helps,
Jan M. Lovell - Secretary
Georgia Domestic Ferret Association
Dedicated to a Better Life for Domestic Ferrets Through Knowledge and
Understanding
770-442-5917
[Posted in FML issue 1679]