The following picture is of a mimic octopus disguising itself as flounder.
My favorite part of the octopus is their many defenses against predators. They are equipped with thousands of organs call chromatophores that allow them to change to a variety of colors instantly. This is very helpful for octopus because it allows them to camouflage and even attract mates. If blending in with its environment isn't enough, then some octopus can even change their texture using small muscles on them that can contract or relax. With the ability to change color and texture instantly, octopus can be very hard to spot. The Mimic Octopus can change color too. However, they don't use their camouflage ability to hide. They actually transform themselves to make them look like other sea creatures like lion fish. As you can see, octopus are well prepared for enemies.
If an octopus needs to escape quickly, they have been known to release a cloud of ink that can acts as a pseudomorph or blind the predator. Some inks might effect the smell of their attackers. This helps octopus escape from predators that require smell for hunting like sharks. Its black or brown coloring is from the pigment, melanin which is founded in many animals. If an octopus does get captured by a predator, then they can break their captured arm off and grow it back later. Sometimes they release an arm before being captured. The released arm crawls around while flashing different colors making itself a decoy while the octopus escapes. Octopus can also attempt to scare away predators by changing color, puffing their bodies, and flattening their arms therefore making them look bigger. Predators are going to have to work for their meal.