 You know, dust gets on siding, be it aluminum or vinyl, and then the morning dew or a little bit of rain or just high humidity gives, that becomes a food source, that dust, and with the mold spores and algae spores in the air, and then the moisture, it's a buffet. And all of a sudden, that nice vinyl siding starts having a greenish tint, and then it gets darker, and before long, it's horrible looking.