Not all slugs (snails without shells) are slimy brown pests found in your backyard garden. In the ocean they come in a huge variety of colors—some match the background and are hard to spot, but others are very conspicuous. Nudibranchs in particular are especially popular with divers and underwater photographers because of their often vibrant and beautiful color patterns. The coloration is useful for more than just a pretty photo, however. Bright colors warn predators that these nudibranchs would make a bad meal because they are armed with toxins and other defenses.