If I were to paint the inside of a coop, I'd go with a darker color myself, although I usually go with bright colors for workshops and storage rooms. Dimmer light seems to help keep the chickens calm. Dimming the light is one remedy to discourage the start of cannibalism. I think the bright light makes it easier for them to see defects or spots to peck at.
Purely personal opinion. Whatever you do will probably workout fine.
Good Luck!!