def gradient_black(
            self, text=None, fore=None, back=None, style=None,
            start=None, step=1, reverse=False,
            linemode=True, movefactor=2, rgb_mode=False):
        """ Return a black and white gradient.
            Arguments:
                text       : String to colorize.
                             This will always be greater than 0.
                fore       : Foreground color, background will be gradient.
                back       : Background color, foreground will be gradient.
                style      : Name of style to use for the gradient.
                start      : Starting 256-color number.
                             The `start` will be adjusted if it is not within
                             bounds.
                             This will always be > 15.
                             This will be adjusted to fit within a 6-length
                             gradient, or the 24-length black/white gradient.
                step       : Number of characters to colorize per color.
                             This allows a "wider" gradient.
                linemode   : Colorize each line in the input.
                             Default: True
                movefactor : Factor for offset increase on each line when
                             using linemode.
                             Minimum value: 0
                             Default: 2
                rgb_mode   : Use true color (rgb) method and codes.
        """
        gradargs = {
            'step': step,
            'fore': fore,
            'back': back,
            'style': style,
            'reverse': reverse,
            'rgb_mode': rgb_mode,
        }

        if linemode:
            gradargs['movefactor'] = 2 if movefactor is None else movefactor
            method = self._gradient_black_lines
        else:
            method = self._gradient_black_line

        if text:
            return self.__class__(
                ''.join((
                    self.data or '',
                    method(
                        text,
                        start or (255 if reverse else 232),
                        **gradargs)
                ))
            )

        # Operating on self.data.
        return self.__class__(
            method(
                self.stripped(),
                start or (255 if reverse else 232),
                **gradargs)
        )