Why marble granite fade?

some stone factory in sales when they declared 'granite' that never fades, but the experiment proved that the granite will fade, just needed some time. Especially in the exposure such as square, metope, the wind and rain on the surface of the granite stone, will change color after 10 days and a half months. So, why are some sellers claim 'never fade'?
expert says granite main mineral is quartz, mica, feldspar, hornblende, pyroxene, etc. These minerals are mainly silicate minerals structure, each surrounded by four oxygen ion silicon ions, constitutes the silicon oxygen tetrahedron. Nature of this structure, stability, acid, strong alkali, dissolved, weathering resistance, good does not change color.
granite fade because of the different varieties. Darker than light-colored granite fade easily, so you should not choose marble, outdoor decoration material as exterior wall act the role of the marble, - Years later the color talks.