Sand Divers, Synodus intermedius can be exceptionally difficult to spot. I have watched an entire group of divers pass within two feet of a Sand Diver and fail to notice it. Sand divers are a type of lizardfish, and like chameleons, they are masters of disguise. A Sand Diver can pale to almost white, or darken to mimic a colorful reef or sponge.
I have always enjoyed watching Sand Divers change their coloration. If you manage to locate a Sand Diver during a dive, gently fan water towards it. Eventually, it will hop to a new place on the reef and immediately adjust its colors to disappear against it background.