This is a 1956 Topps Hank Aaron Gray Back PSA 4. The Gray backs are actually slightly less common than the white backs among the first 100 cards of the 56 set. For cards 101+, the white backs are the hard ones to find. This is a great card and I'm sure the winning bidder will be happy with it.
The winning bidder for this auction will receive the card promptly and well packaged.