I assume the squirrel's that make a daily visit to my abode are British Greys, after all they were born here in the UK ;o)
I don't know if its possible, but I have noticed a little bit of red in the colouring!!.
Regarding the FE's comment about Chipmunks climbing trees. A friend use to breed and keep these critters amongst other things, and on one occasion, one decided (on handling) to bite my hand and do an hasty super fast retreat up a nearby tree. I wish I could move as fast as that did on that day. Yes we did catch it finally, after over an hour of frenzied activity :O(