How does Paul Auster use imagery in City of Glass?

Imagery:

First of all there is Blue. Later there is White, and then there is Black, and before the beginning there is Brown. Brown broke him in, Brown taught him the ropes, and when Brown grew old, Blue took over. That is how it begins. The place is New York, the time is the present, and neither one will every change. Blue goes to his office every day and sits at his desk, waiting for something to happen. For a long time nothing does, and then a man named White walks through the door, and that is how it begins.