What is not clear??? It is of course polycarbonate but on its upper surface is a matt paint…and that is all.. When you deformate the cover the paint layer can be peeled off( you can do it even the cover is not deformated - if you use a thinner the layer will be washed off) So the deformated paint makes thouse grey spots. The same effect has in the course of time aggressive sweat. The blue and pikn variants of nokia do not have such a layer. And as to my technical inteligence. I work in a service centre of Nokia