What if animals could change color like an octopus?

An octopus can be brown, then red, then bumpy and gray, all in a moment! It can look just like a rock.

What if other animals could change color like that? What if a cat or a bird could?

The Smithsonian calls cephalopods, the group that includes octopuses, squids and cuttlefish, the 'chameleons of the sea'. They can change the color and even the bumpy texture of their skin in the blink of an eye.

Imagine a zebra swapping its stripes for spots, or a robin turning leaf-green to hide in a tree. So what if many more animals could change color like an octopus? This lab is a thought experiment. Follow three paths: hiding in plain sight, sending signals, and the color cells in the skin.

Cephalopods achieve rapid color change with skin organs controlled by muscles and nerves, and some lizards, such as chameleons, with a quite different mechanism. Both are used for camouflage and for display.

This thought experiment asks what might change if rapid color change were widespread: for predators and prey, for communication, and for the animals' energy budgets. The skin mechanisms are established science; the consequences for an imagined world are labeled as ideas.

An octopus has thousands of tiny color bags in its skin. Each one can open wide or shrink small.

When they open, we see red, brown or yellow. When they shrink, the color hides.

The Smithsonian explains how cephalopods do it. Their skin is dotted with thousands of tiny color cells called chromatophores. Each has a stretchy bag of pigment controlled by muscles and nerves. When the muscles pull, the bag opens wide and shows red, brown or yellow. When they relax, it shrinks and the color hides.

Under the chromatophores, other cells called iridophores make shiny greens, blues, gold and silver, and white cells called leucophores reflect the light around them. Tiny bumps called papillae change the skin's texture too.

Each chromatophore is an elastic, pigment-filled sac connected to several muscles and nerves; contraction expands the sac to show red, brown or yellow pigment, and relaxation hides it (Smithsonian). Iridophores beneath produce metallic greens, blues, gold and silver; leucophores scatter ambient light and are believed to aid camouflage. Papillae alter skin texture, and a 2018 study found cuttlefish papillae lock once extended, holding a textured disguise at little energy cost.

Chameleons work differently. University of Geneva researchers showed in 2015 that panther chameleons change color by actively tuning a lattice of nanocrystals in skin cells called iridophores, rather than by spreading pigment.

Imagine a world where lots of animals change color like an octopus.

A rabbit might look like the grass. A fish might look like the sand. It might be very hard to find anyone!

Imagine a meadow, a forest and a reef where many animals could change color in a moment. A rabbit might match the grass beneath it, then the dirt path a moment later. Hunters might hide better too, so hiding would help both sides.

Animals might also 'talk' in color more often, flashing patterns at each other the way cuttlefish do. But there could be a catch. Scientists have found that octopus color change uses a lot of energy, so these animals might need to eat more, or rest more, to pay for it.

Widespread rapid color change might intensify the contest between camouflaged prey and camouflaged predators, as each could match changing backgrounds. Signaling might grow richer too, as in cuttlefish, whose patterns help them communicate.

The constraint is energy. Sonner and Onthank (PNAS, 2024) estimated that activating all of a ruby octopus's chromatophores at once would cost almost as much as its resting metabolic rate. Walla Walla University notes this may push octopuses toward dens or night activity, and may relate to reduced chromatophore systems in deep-sea species. Animals that changed color constantly might need more food, or might change color sparingly. These are ideas, not predictions.

Changing color helps an octopus hide from animals that want to eat it.

It also helps an octopus sneak up on its food. Some animals use bright colors to say, 'Stay away!'

The Smithsonian says some cephalopods use color change to blend into their surroundings, while others do the opposite and stand out with a flashy display. Cuttlefish in experiments by the scientist Roger Hanlon have copied mottled textures, stripes, spots, and even a black and white checkerboard.

The flamboyant cuttlefish shows the other use. Monterey Bay Aquarium explains that instead of darting away when threatened, it stays still and flashes bright colors, which may warn predators. Its patterns also help it communicate with other cuttlefish.

Color change serves two opposite goals. Camouflage: by combining color, texture and posture, cephalopods can match almost any background, and Roger Hanlon's experiments showed cuttlefish matching mottle, stripes, spots and even a checkerboard. Display: other species stand out deliberately (Smithsonian).

The flamboyant cuttlefish remains still and flashes bold colors when threatened; Monterey Bay Aquarium notes this may be a warning to predators, since a toxicology study found its muscle tissue highly poisonous, and that its patterns also help it communicate. The mimic octopus goes further, appearing to imitate up to 15 other animals.

Chameleons are lizards that can change color too.

But they do it a different way. Tiny crystals in their skin bounce back different colors of light.

Octopuses are not the only color changers. Chameleons, a group of lizards, change color during encounters with other chameleons. University of Geneva scientists discovered how in 2015: chameleon skin holds a layer of cells packed with tiny crystals. By changing the spacing of the crystals, a chameleon changes which colors of light bounce back.

The researchers found a deeper layer of crystals too, which reflects infrared light. They say the two layers let chameleons switch quickly between good camouflage and a spectacular display, while also helping protect them from heat.

The University of Geneva team led by Michel Milinkovitch and Dirk van der Marel (Nature Communications, 2015) showed that chameleons' rapid color changes during social interactions come from actively tuning a lattice of nanocrystals in a superficial layer of iridophores. A deeper iridophore layer with larger, less ordered crystals reflects infrared light.

They describe the two-layer arrangement as an evolutionary novelty that lets chameleons shift rapidly between camouflage and display while giving passive thermal protection. Octopuses and chameleons thus reached color change by unrelated routes: muscular pigment sacs in one, structural color in the other.