f

mon = peripheral.wrap("top")
mon.setBackgroundColor(colors.black)
mon.clear()

function BoxL (xmin,xmax,ymin,ymax,rows,color1,color2)
  local currColor = color1
  for k = 0,rows do
    if currColor == color1 then
      currColor = color2
      mon.setBackgroundColor(currColor)
    else
      currColor = color1
      mon.setBackgroundColor(currColor)
    end
    for i = xmin,xmax do
      for j = ymin,ymax do
        mon.setCursorPos(i,j)
        mon.write(" ")
      end
      i = i + 1
    end
    k = k + 1
    mon.setBackgroundColor(colors.black)
  end
end

BoxL(1,20,1,2,2,colors.red,colors.blue)