Shingles primarily get their color from the granules. The granular color is colorfast or non bleachable.
And I have seen strong mixes cause some minor "bleaching" of fiberglass shingles.
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Matthew C Perry General Manager Callahan Pro Wash Professional Exterior Cleaning Services Roof Cleaning, Pressure Washing, Paver Cleaning and Restoration 813-727-5161 callahanprowash.gmail.com