I have had a little trouble gaining an understanding on the color vision of chickens. But, it's the owl that sees everything in shades of gray.
One fellow that I read says that chickens have only cones in their retinas. This is why they have such poor night vision but it would mean that they see everything in colors
Obviously, they see differently than humans do. Low light in the red part of the spectrum seems to be good enuf for a chicken and they can still function. Blue light is good enuf for us and not so good for the chicken.
Bright light encourages pecking probably because it helps the chicken see a spot more easily. But, it has been known for a long time, that chickens respond to all colors and can distinguish one from another. Still, chicks peck at spots of different colors with almost equal interest. There's not much reasoning going on in the reflex. If a spot is green or blue or red - it gets a peck.