Blue’s scarcity in nature may have helped shape our perception of the color and things that appear blue. "With blue, it's like a whole canvas that you can still paint on," Kupferschmidt said.

While humans have three color cones in the retina sensitive to red, green and blue light, birds have a fourth color cone that can detect ultraviolet light. A Princeton-led research team trained wild ...

These light receptors do not perceive color, but they are sensitive to light and dark changes, as well as shape and movement. And the ratio of rods to cones in the retina is much higher in dogs ...