If it is unplated (and it does not look that way, but that may be your pix), it is unplated because someone has dipped it in acid.
I think1983 to 2003 the mint planchet maker of cent was get the copper mix wrong. there called brassy cents Value????
not unplated, it would be gray in color. if anything, possible brass plated, so the difference in color. only valuable to dealers who promote that type of error.