As you would expect, fish that rely on camouflage for protection are hard to spot when they’re at rest. The best bet to see them is to spot them on the move.
Sometimes I notice the final motion of one of these creatures before it settles in one spot and blends in. In this case, this flowery flounder was trucking along over a sandy bottom for quite some distance before it rested on the sand. Even in motion, and casting a shadow, it’s easy to see how hard it will be to spot this fish when it stops on the sand below.