Oxidation in a 16 month old Brown Velvet, see circled areas.
Oxidization happens with all forms of hair/fur. In chinchillas, it is most noticable in Beige and ebony crosses, violets, and very dark standards. Only sapphires never appear to oxidize.
This one year old ebony is showing it on his belly. Oxidization is the discolorization of the fur with exposure to the elements. It sets in after a year of age in most animals. In humans it creats those desireable natural highlights.