Hit the right button on your speedometer, it'll adjust the screen brightness. There are 4 brightness settings.
If you want to go the paper route, I'd recommend velcro as that's non-destructive as compared to adhesive. A more aesthetically pleasing option would be to change your speedometer face.
http://www.smartcarofamerica.com/forums/f19/speedometer-faces-44150/
http://www.smartcarofamerica.com/forums/f19/speedometer-faces-44150/