I've been cutting up and slicing some blue foam lately, and while cleaning up, I decided to pick up the little leftover "crumb" pieces of foam and saved them in a plastic container. Can these little foam crumbs be used as rocks/talus/boulders? In N-scale they range from beachball-size to half the size of a human figure. Has anyone used foam pieces like that before? How do I paint/dye them into a rock color?