A type of Silver Fox .... basically a Red Fox with a genetic mutation that alters its usual red fur colouring with a darker brown or black colour.

https://en.wikipedia.org/wiki/Silver_fox_(animal)

I'm Ojibway from northern Ontario and we always identified these guys according to colour ... Red Fox, Black Fox or White Fox (aka Arctic Fox) ... I know Arctic Fox is a separate species and it is rare in my area but we still see it as its a cousin to the Red/Black variety.