It looks like a note that was rubbing up against another for a long period of time like in a wallet. If you take a Birds or Multicolour note and rub it against a piece of plain white paper you will see some colour transfer.
That being said, if you ever find anything you don't know about, show it to someone that has lots of experience in collecting bank notes, or a trusted dealer for an opinion. Having it in hand always gets the best review. Its always a learning experience.