In Spain most roof are made of spanish roof tiles, and by time these tend to be attacked by agle and other organic materials, all depending on humidity, exposure to sunlight etc. and its is very common to see houses with almost all dark roofs even tho they have been terracotta colored at some point.
Organic material do affect the lifespan of the materials they attach to, and to clean your roof is to expand the lifspan of the roof, we clean tiled roofs with a combination of pressure and chemicals so the growth will not start to come back again soon after the cleaning.
But all roofs are different and the quality of the materials and the quality of the construction of the roof will decide in what way it can be cleaned. If you have a original teracotta colored roof, we can help you bring the colors back!
Of course we clean all kinds of roofs, what ever material they are made of. In the cases its possible we will avoid walking on the roof, and use tools and equipment to work in a effective and safe way, without standing on the tiles.