The loaner helmets are for whatever, you just need to only borrow it when your driving/riding. If your not behind the wheel/riding put the helmet back, they have a problem with loaners being borrowed all day and their aren't enough for everyone.
Make sure you use the "Painters" type masking tape, the other stuff will leave a nasty residue on your paint. Most any color is good as long as it's visible and the numbers/letters are legible.