An octopus blending into a rough background is doing something more interesting than choosing a matching paint. Its visible appearance involves different skin structures, and sometimes changes of texture as well as colour.
The Smithsonian’s explanation of cephalopod colour change describes pigment-containing chromatophores controlled through muscles and nerves. It also discusses reflecting structures and the projections called papillae that can alter an octopus’s skin texture.
Try watching a clearly identified animal in a documented video. Choose a short sequence and record three things separately: the colour pattern, the apparent surface texture and the animal’s posture. You may notice one changing before another.
Avoid giving every change one motive
A video may show an animal becoming conspicuous rather than disappearing into its surroundings. The surrounding context and species-specific account matter. A visual change alone is not a complete explanation of what the animal perceived or intended.
Do not approach, handle or provoke marine life to produce a demonstration. Existing research and aquarium material can provide a much better view without creating a disturbance.
In a notebook, write the observed sequence first and the documented mechanism underneath. That keeps a remarkable biological process from becoming a vague claim that an octopus can simply turn into anything it wants.
Editorial illustration from this site’s image library; not documentary evidence of the example or object discussed.