The blue-ringed octopus will, out of fear, produce blue-colored rings all over its body to warn predators to steer clear. These rings have been given the name “blue rings of death” for a reason. If this cute little octopus bites you, you will instantly succumb to its lethal venom. Within minutes you could perish due to heart or lung failure thanks to this octopus’s signal (the same signals sent from to your brain throughout you body telling its parts what to do) blocking venom. This octopus is able to warn predators thanks to “chromatophores” which are cells that contain pigment. So, the octopus does not actually change color. Instead, it inflates its body in such a way as to make its blue rings of death more obvious to potential predators. Other animals have been known to use chromatophores to induce ‘color-changing’ effects like the chameleon or the cuttlefish.
Check out the following sources for more information!
https://ocean.si.edu/ocean-life/invertebrates/how-octopuses-and-squids-change-color
“Venomous” book by Christie Wilcox
Life through green tinted glasses 