As long as the caulking is good and there are no tears or leaks in the roofing material, a little off white color does nothing for your rig. If you start using abrasives, including Soft Scrub, which is still an abrasive cleaner, you will start removing the white portion of the roofing, and ultimately, you will end up needing a new and very expensive roof. Unless you are above the roof looking down, you really can't see the roof, so why worry about it.
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