I note that the yellow Royal Inn fob you show has black printing, mine has gold; so my roommate's theory may be right. He postulated: Royal Inn (and Barbary Coast) had a bucket of different-colored fobs beside the registration desk with a sign reading something like: "Take One - With Our Compliments."

Royal Inn and Barbary Coast were both owned by Michael Gaughan so maybe he personally cut out each plastic fob for his guests. (Ya think?????)