Cleaning leaf stains off outside panels.

Unfortunately, we don't store our pop up inside during the winter. I store it beside our garage. The problem is that all the run off from the roof falls on to the roof of the camper. I don't already go out and clean the roof off. So I have orange stains from the leaves that sit on the roof all winter. I've pressure washed the camper to remove the black stuff but the leaf residue is tough to get off. What can I use to remove the stains?