Hi again, I do not know what to call this? very strange and rare. Has anyone seen anything like this before?
With out it being in hand we can only guess, it looks like some foreign matter that attached to the coin after it left the mint and entered circulation.
Something had stained that Cent. It's made of zinc and coated with a very thin layer of copper. Zinc Cents are terrible. Not a mint error and only worth one cent. Welcome to CT.
I am serious also.. It is a dirty coin There are millions of coins in circulation that are dirty. You found one. It is nothing special.