The silver fox is a melanistic form of red fox. Melanism is when the animal's coloring is much darker than normal. Interestingly, fox squirrels, who have brownish body fur and reddish tummy fur also have a melanistic form that resembles this.
The Fox Squirrel, Sciurus Niger, is the largest species of tree squirrel native to N. The most common Squirrel in my area by far. There ins't a thing you can do about them. They're tenacious survivors.