Yes, I saw a documentary that mentioned these foxes. The pelts went from being a beautiful golden red to almost black.
And rough and patchy, instead of thick and soft.
It’s interesting that adrenaline levels correlate with the great pelts. It’s been found that sheep and goats produce the finest hair, such as the real Kashmiri wool or the hair of Andean vicunas, only when they’re on the edge of survival due to minimal food, cold temperatures, and low oxygen levels.
If you take the same animal and put it in a more pleasant environment, you get lower quality hair. (The vicunas just die.)