Originally Posted by fsumotorhead
I thought the black discoloration on light colored shingles was a form of algae, I hit some dark spots on my old house with oxygen bleach, shit came right off.
These are caused by a defect in the shingles. Some about iron oxide or some such thing. I do not remember right now what the actual cause was but I just know it was nto real cheap to have the roof done and shingles start changing colors maybew 5 years later. Might not have been even that long.