How do chromatophores allow cephalopods to change color quickly?

Cephalopods are capable of rapid color changes—often occurring in half a second or less—due to the unique structure and neural control of their chromatophores.1

Unlike the cellular chromatophores found in vertebrates, which often rely on hormonal regulation, the chromatophoric organs of cephalopods function through direct neural stimulation. Each organ consists of an elastic sac filled with biochrome (pigment) that is surrounded by a ring of radiating muscle fibers.12

When the animal's brain sends a signal, these muscles contract, stretching the pigment sac into a broad, thin disk that makes the color visible. When the muscles relax, the sac shrinks, concealing the pigment and effectively making that area of the skin appear lighter or transparent. By coordinating these muscular contractions across their skin, cephalopods can create complex, rippling patterns used for camouflage, defense, or communication.231