Well, this is a new one for me. We have a LOT of Gray Squirrels around here. Once had one with white patches. Whether it was pinto-spotted or white from injuries, I don't know.
But this clairol-touched fella isn't like anything I've seen before!!
Sorry about the cut-off nose, but I include this picture to show the extent of the red coloration.
I found some google references to melanistic (black) Grey Squirrels having red tails, but couldn't find any pictures, nor any reference to a normal grey-phase having a red tail.