Spectacular bird’s-eye view? Hummingbirds see diverse colors humans can only imagine: Team trains wild hummingbirds to discriminate UV color combinations 

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 research team trained wild hummingbirds to perform a series of experiments that revealed that the tiny birds also see combination colors like ultraviolet+green and ultraviolet+red.

Source: Spectacular bird’s-eye view? Hummingbirds see diverse colors humans can only imagine: Team trains wild hummingbirds to discriminate UV color combinations — ScienceDaily