It sounds similar to the Kaibab squirrel found on the Kiabab Plateau of Arizona. This is a pure white sqirrel with a jet black tail. The Kaibab Plateau is just above the north rim of the grand canyon and these squirrels are everywhere. They get their coloring from the white bark birch trees and the near black bark of the fir trees. The kiabab deer are some of the biggest that I have ever seen. If your ever near there drive to the north rim.