Stop in for a cup of coffee
Me and a buddy in High School used to box trap squirrels all over the county and then snuff them and sell the tails to a fly-tying company and the meat to the poor folks down in the city. Once in a while, we would get a black squirrel in the trap. For giggles, we decided to release the black squirrels on the local country club golf course. After a few years of doing this (plus trapping the grey squirrels off the course), the entire population of squirrels at the country club were black and began to spread beyond there into the surrounding neighborhoods.
To this day, the District Conservation office has never figured out why there is a widespread population of black squirrels in this part of the county.