Well, some things that come to mind:

Are there any spots that are different on the noses? Once you look, you
might be surprised. Also, some ferrets have different colored hairs
coming off the tips of their ears. Some sables have white, some black.

Of course, the boy and girl thing should help. Just flip over and boom,
belly button is the boy.

If you had two girls or two lookalike boys, check for tattoo marks on
the toes, if they are Marshalls. Some have them, some don't - they're
from the vet or "helper" who did the spay/neuter, supposedly. These can
be quick ways if one has the tatts and the other doesn't.

Other than that, a bit of food coloring on the nails will work. Every
few days you can dab some coloring on a q-tip and dye the nails. Some
ferrets have the color last a while. Some don't, depending on the age
and amount of digging and grooming they do. I find the nail coloring
much MUCH easier and reliable than dying the fur itself. However, you
can go that route, but on sables it's hard to have a color stand out
on the fur!

Laryssa

[Posted in FML 6473]