I should have been more clear, the roof is supposed to be pink, it is like a pink/red colored shingle. We live in wisconsin where we have all four seasons, and the part of the roof where it is stained with black mold, is completely free of any trees, it just faces north. Luckily, it is in the back of the house. If I mix one part to one gallon, it won't discolor the shingles or leave white bleach marks will it? There are also no shrubs beneath that part of the roof, so do I still need to wait until winter to do it?