f5b8619d ​

let g: OList OList Color

let input = g

let output = g
  |> hview
  |> map (λg. if (all (eq black) (flat g)) g
    (map (map (λc. if (c == black) teal c)) g))
  |> hcat
  |> (λg. flat [g, g])
  |> (λg. hcat [g, g])