They are nocturnal predators and can see in light at least three times dimmer than people can. Owls evolved to prey on small mammals, which were originally nocturnal to stay out of the way of the cold-blooded reptiles. Most mammals have very few cones if any. Most also have fur that is earth tone in color. Neither predators nor prey want to stand out.
Birds generally have excellent color vision.
This should not be surprising because they evolved from reptiles that are active in daytime. Also, like many insects, they seek flowers for pollen or nectar and flowers evolved colors to stand out from other vegetation. Color vision also enables birds to use color for other purposes. Many birds are very colorful - especially the males whose displays can attract mates, drive off rivals, and draw predators away from a nest where a drab female sits motionless. In August, mallards lose their flight feathers.