If you have a EPDM roof and the black spots don't come off when you clean the roof the spots are probably the black EPDM under layer beginning to show and not mold. The white top layer will slough off over the years and multiple roof washings and eventually just leave the black under layer exposed. My friend has the same year MH as mine and his roof is entirely black. Another friend gave me some Cool Seal roof coating 10 years ago which he no longer needed when he bought a new MH with a FG roof. I had enough to apply a primer coat and one top coat. It lasted for about 5 years and is almost all worn off. The bottom line is the coating sloughed off instead of the roof material itself extending the life of the roof.