Marine mammals have a reflective layer behind the retina of their eye called tapetum lucidum, which is Latin for “bright tapestry”. It is this same reflective layer that causes the eyes of cats to glow at night. This layer enhances the ability of an animal to see under low light conditions by reflecting light back through the retina a second time, making the most of available light.
The retina of baleen whale’s eyes contains mostly rod cells, which are sensitive to low intensity light, while cone cells, which distinguish between different colors and are most sensitive to bright light, are less abundant. This means that whales are most likely to see the world in shades of grey.