Many people think the silver fox is a species related to the red fox. But they are the same species. The silver fox looks so different to the red because of something called melanism. Effectively, this is the opposite of albinism - it is the development of a dark pigment in the skin or fur of animals.
So, although a silver fox may look like a visiting relative it is still the Vulpes vulpes that we see more regularly in its red form. However, the rarity of this melanistic mutation has meant that throughout history the silver fox has been even more persecuted than its red counterpart.