The Moorish Idol, Zanclus cornutus, has white, yellow, and black bars which break up its coloration, making it harder for predators to tell where the fish begins and ends. It got its name from the Moors of Africa, who believed this fish would bring them happiness.
Perhaps that’s why they’re so popular as aquarium fish. They’re notoriously hard to keep in captivity, though, because they’re extremely selective eaters.
Sea hares also have a reputation for being hard to keep alive in tanks because of their very specific water requirements. That’s why they’re only recommended for advanced aquarists (which I am certainly not… but my hares live surprisingly long; we’re going on over 6 months now!) In any case, they’ll always be my “bringers of happiness.”