You may wish to cover your walls with writing and graffiti. This is probably unappealing for future occupants of the room and Food and Housing has to repaint the walls. Finally, your choice of colors may not be the first or any choice of the future occupants of your room. Any unauthorized painting will be repaired at the end of the year, at the expense of the occupants. Do not put any nails or screws in the walls.
Holes are expensive to repair and unsightly even after they have been filled and painted.