834ec97d ​

input = fill #0 (fill #1 black) |> rect ((#2, #3, #2, #3), #4)
output = fill #0 (fill #1 black) |> fold (λr. rect ((1v, r, #2, r), yellow)) #5 |> rect ((#2 + 1, #3, #2 + 1, #3), #4)
(VInt, HInt, VInt, HInt, Color, UList HInt)
(3v, 3h, 1v, 2h, red, {2h})
(5v, 5h, 3v, 3h, fuschia, {5h, 3h, 1h})
(9v, 9h, 5v, 3h, brown, {9h, 7h, 5h, 3h, 1h})
(12v, 12h, 4v, 6h, green, ?)