Well, close your eyes and trace the edge of your keyboard or something similar. Obviously you know what it looks like, but just ignore that, and ignore what color it is. When I trace it, I see no real image. Instead, it is more like I am making a 3-D map. Now, maybe the mind might assign arbitrary colors to the map to produce an image of the map (and use different colors/shades to separate objects), but I think it is more emphasis on memorization of a 3-D map.
A good example, walk around your house at night without the lights on and maybe your eyes closed, and do it slowly. You'll probably start remembering the layout of furniture and feel for objects and walls that you are familiar with seeing. Now, this method should work for both a blind and non-blind person, the only difference being the primary sense used to learn the layout (touch vs. seeing).