code: def tint(col, factor=1.0):
      
      # this method is more complicated than it need be to
      # support matplotlib-1.x.
      # for matplotlib-2.x this would just be
      #     h, s, v = colors.rgb_to_hsv(colors.to_rgb(c))
      #     v *= factor
      #     return colors.hsv_to_rgb((h, s, v))
      rgb = numpy.array(to_rgb(col), ndmin=3)
      hsv = colors.rgb_to_hsv(rgb)
      hsv[-1][-1][2] *= factor
      return colors.hsv_to_rgb(hsv)[-1][-1]
docs: Tint a color (make it darker), returning a new RGB array