The promise of Jesus to those believers in Pergamum who overcome was that he would “give him a white stone (psephos) with a new name written on it, known only to him who receives it” (Revelation 2.17). This promise is to be understood in the local setting of the church in Pergamum.
The Hellenistic buildings on Pergamum were built of the local dark colored granite, called andesite. Because of its dark color, marble was imported for inscriptions, so that they could be read clearly. In this picture, the contrast between the dark local stone and the white marble is dramatic and if you want your name to be remembered you want it written on a white stone and not on a black one!