Is this a cooper quarter?
Post-minting damage. Not an error.
Your coin suffered environmental damage. Many times, clad coins with that type of discoloration are metal detector or ground finds. There can be a lot of different chemical reactions that can stain a coin. Your coin didn't leave the mint looking like that and isn't an error
BTW, if it was struck on a planchet that was missing the clad layer on both sides it would be seriously thin and underweight.
A environmental damaged quarter.