code: def gradient_rgb(
              self, text=None, fore=None, back=None, style=None,
              start=None, stop=None, step=1, linemode=True, movefactor=0):
          
          gradargs = {
              'step': step,
              'fore': fore,
              'back': back,
              'style': style,
          }
          start = start or (0, 0, 0)
          stop = stop or (255, 255, 255)
          if linemode:
              method = self._gradient_rgb_lines
              gradargs['movefactor'] = movefactor
          else:
              method = self._gradient_rgb_line
  
          if text:
              return self.__class__(
                  ''.join((
                      self.data or '',
                      method(
                          text,
                          start,
                          stop,
                          **gradargs
                      ),
                  ))
              )
  
          # Operating on self.data.
          return self.__class__(
              method(
                  self.stripped(),
                  start,
                  stop,
                  **gradargs
              )
          )
docs: Return a black and white gradient.
              Arguments:
                  text       : String to colorize.
                  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 rgb value.
                  stop       : Stopping rgb value.
                  step       : Number of characters to colorize per color.
                               This allows a "wider" gradient.
                               This will always be greater than 0.
                  linemode   : Colorize each line in the input.
                               Default: True
                  movefactor : Amount to shift gradient for each line when
                               `linemode` is set.