I've got a whole backyard full of "black" squirrels. Seems to be more prevalent in urban settings(I live in a sub-division on the outskirts of town) when squirrels tend to interbreed. Some claim it's a recessive gene that dates back to before squirrels broke into the sub-species of grey and fox squirrels. At one time having black fur kept small bodied squirrels warmer in the winter. Supposedly the gene was passed from Fox squirrels to Eastern Greys thru interbreeding between the two species and now is passed by inbreeding within the grey squirrel species. All of the "black" squirrels in my backyard appear to be Greys, even tho there are some Fox Squirrels back there too. The amount of "blacks" seems to come and go. Some years we have only one or two, this year we appear to have at least 4 since I have seen 4 at the feeders at one time. Always a disappointment to see a "blackie" flattened on the county road that runs behind us. Kinda like finding the red feathers of a Cardinal on the ground beneath the feeder after the neighborhood feral cat or the local Sharp-Shinned gets it.