Ok, I asked before on Facebook, but I still don't get it.
What is "brun"???
Is it just any brown rabbit?
Or mutt rabbits?
A mythical breed of rabbit?
???
They are related to the champagne d'argent (black based with silver), creme d'argent(red based with silver), and Argente bleu (blue based with silver). There is also a st hubert which is a chestnut with silvering but they aren't recognized too many places.