Albino and Piebald Grey Squirrels
Above is an albino Grey Squirrel, showing pink eyes and claws as well as totally white fur.
Albinos occur naturally but rarely. There is also a race of melanistic Grey Squirrels with a gene for black fur (jet black or very dark brown). Several populations of black Grey Squirrels (Eastern Gray) exist in the US, Canada and in southern UK (north Hertfordshire, Cambridgeshire). Because the black gene is dominant, they are increasing their range at the expense of greys.
Occasionally Grey Squirrels will have white patches on their fur (topside, since the underside is normally white) or be piebald (large expanses of white and of grey).