code: def _gradient_black_line(
              self, text, start, step=1,
              fore=None, back=None, style=None, reverse=False, rgb_mode=False):
          
          if start < 232:
              start = 232
          elif start > 255:
              start = 255
          if reverse:
              codes = list(range(start, 231, -1))
          else:
              codes = list(range(start, 256))
          return ''.join((
              self._iter_text_wave(
                  text,
                  codes,
                  step=step,
                  fore=fore,
                  back=back,
                  style=style,
                  rgb_mode=rgb_mode
              )
          ))
docs: Yield colorized characters,
              within the 24-length black gradient.