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. I had a "black" fox squirrel that I hand raised. He lived to be 12 years old, a full ten years longer than he would have in the wild.
Foxes are known to have both canine and feline characteristics. Even though they are considered to be a member of the dog family, they have feline characteristics such as vertically slit eyes and retractable claws. They are excellent tree climbers and also play with their prey before killing it, just like a cat.