In human eyes, we have two basic kinds of photoreceptors. Rods allow us to see lights and darks (grayscale), and cones allow us to see color. Cephalopods such as octopuses, squids, and cuttlefish (in the painting) have only one type of photoreceptor–for sharp images, but in grayscale. This renders them technically colorblind. But how are these invertebrates able to change their color to match their environment, if they cannot see color?
Research published in 2016 concludes that the movable, off-axis position of cephalopod pupils allows the creatures to vary their focus on different sections of the scene before them. In addition, the odd shapes typical of cephalopod pupils (W, U, or dumbbell) allows light to enter the lens from all around instead of straight into the retina. This allows the animals to focus on a
Ink, watercolor, and gel pen on paper, 6″x6″.