Environmental damage.- the grey. One above same zinc rot. @paddyman98 can show all various color pennies from metal detecting.
The grey cent has had the copper removed. I bet it is slightly larger in diameter than other cents. People will put them between leather and hit them with a hammer. The thin copper coating falls away and you are left with a grey zinc cent. They are often called Texas cents.
@Goldsayshi463 Any cent minted mid 1982 are Copper plated zinc. They have all sorts of plating, exposed plating and zinc issues that have occured after it left the Mint. Thats why we call them Crappy Zincolns. We will do our best to answer your questions but sometimes the stuff you show is obvious.