A ferret that is a dark eyed white at birth is very rare.  This means NO
stray dark fur anywhere onthe coat.  I used to be able to breed these, but
the male passing on the gene passed away and I kept a daughter who ended up
being sterile.  So I lost the line.  BEW females tend to either be poor
mothers, canibalistic or infertile, hence the "color" being so hard to
perpatuate.
 
NOW - light silvers, those ferrets with dark eyes and a few or more dark
hairs tend to go lighter as they get older, especially after they are
altered.  Really light silvers can become dark eyed whites in a year or
two - that is why several ferret showing systems allow ferrets with a few
dark hairs to be entered in the dark eyed rings - they will get that way
eventually and the show sponsors do not want the owners to pluck out the
odd dark furs and cause discomfort to the ferret just for a silly show.
For an example - look at the earlier issues of Modern Ferret and Knuks -
he was a dark eyed stripe.  Now look at more recent photos (I think issue
#5 gives baby and adult photos) and his stripe is gone.
 
Pandas - I have had several silver pandas in my breeding lines, and as soon
as I get them spayed or neutered, they turn almost white.  Pandas usually
have a few dark patches on their original coats which stay put after the
rest of the coat has lightened up, hence the "pattern" category at several
shows.  I have a striking photo of one of my ferrets at 2 years of age.
Patches was a silver panda - a VERY distinct dark coat, white feet, white
head with a dark patch behind her ears.  this ferret is now almost 8 and a
half, and with the exception of the patch, she is white.  Last night I was
visiting friends (Hi Rhonda and Bruce) and asked to see Buttons, another
retired silver panda breeder I had spayed and adopted to them.  A BEW was
pulled out and handed to me - and Buttons was a medium silver coat whan I
had her spayed a year ago.  Buttons is a grandmother now to her albino
daughter's litter of 6 cinnamons.  Genetics are a funny thing.
 
Silvers are not rare, they just keep changing coats.
 
Pam
[Posted in FML issue 1532]