Being from New England I was very familiar with grey and red squirrels (flying ones as well). The black squirrel (a melanistic subgroup of grey squirrel) was not something I had seen before. The original population here was imported (by John Harvey Kellogg) to MSU back in the day. When I first moved to town they were still primarily located on campus and the surrounding environs. I am about 3 miles from campus and it has taken about 25 years for the majority population to tip in favor of the black.
The three flavors of squirrel do not like each other. I don't know who won this battle but I'm betting on the black squirrels. I'm also betting that there will be new walnut trees sprouting all over my yard AGAIN!