Concrete and clay tiles use a pigment for coloring, some are organic which fade. The coloring is measured and mixed in by weight and is dependent of say the concrete in concrete tile to act as the glue and hold it in place. Most pigments used today are synthetic or iron oxide, which do not tend to fade. However an acrylic sealer is also added to the tiles during the manufacturing process. This sealer naturally wears with agenda exposes aggregates, moves color pigments and traps dirt. Having your roof cleaned with high pressure accelerates this process causing your tiles to appear dull in color without shine and/or appears different than when originally installed.