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How quickly can cephalopods change colour?

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A blue-ringed octopus with bright blue rings on its beige body crawls over a rocky, coral-strewn seabed. — cephalopod Blue-ringed octopus (genus *Hapalochlaena*).

Cephalopods are capable of remarkably rapid colour changes, often completing these shifts in half a second or less.1

This speed is achieved through the use of specialized organs called chromatophores. Unlike many vertebrates, which rely on slower hormonal processes, cephalopods control their chromatophores directly through the nervous system. Each chromatophore consists of an elastic sac filled with pigment that is surrounded by a ring of radiating muscle fibres. When these muscles receive neural stimulation, they contract, stretching the sac into a broad, thin disk that displays the colour.12

This physiological mechanism allows for spectacular, near-instantaneous displays, with waves of colour rippling across the animal's body in response to various behavioral conditions, such as camouflage, defense, or alarm.13