...Or starts changing colour suddenly. In a sunlight it is iridescent, yet in dusk there is not much light to reflect with a skin, so it mostly gets pale and darker. A camera flash makes them greenish, a shot in natural light would show them as smoky-gray.

This is a usual pose for octopus to sit in, spreading it's hands to touch or to taste something (octopuses have a special chemo-tactile receptors on their suckers).