The silver fox is a melanistic form of the red fox. They can be almost completely black, more silver in appearance, or even a bit bluish grey. Their skins have historically been the most sought after by fur traders and were fashionable to nobles in Russia, western Europe and China. In the wild, they occur alongside the more commonly colored red red foxes, and they are born into mixed litters. I came across this silver fox late one afternoon while hiking in Mount Rainier National Park in Washington.
Nikon D300 with Nikkor 200-400mm lens (at 400mm) ISO 800, f/5.6 at 1/400th of a second (-2/3 stop ev)