code: def add_chan(self, chan, color=None, values=None, limits_c=None,
                   colormap=CHAN_COLORMAP, alpha=None, colorbar=False):
          
          # reuse previous limits
          if limits_c is None and self._chan_limits is not None:
              limits_c = self._chan_limits
  
          chan_colors, limits = _prepare_colors(color=color, values=values,
                                                limits_c=limits_c,
                                                colormap=colormap, alpha=alpha,
                                                chan=chan)
  
          self._chan_limits = limits
  
          xyz = chan.return_xyz()
          marker = Markers()
          marker.set_data(pos=xyz, size=CHAN_SIZE, face_color=chan_colors)
          self._add_mesh(marker)
  
          if colorbar:
              self._view.add(_colorbar_for_surf(colormap, limits))
docs: Add channels to visualization
  
          Parameters
          ----------
          chan : instance of Channels
              channels to plot
          color : tuple
              3-, 4-element tuple, representing RGB and alpha, between 0 and 1
          values : ndarray
              array with values for each channel
          limits_c : tuple of 2 floats, optional
              min and max values to normalize the color
          colormap : str
              one of the colormaps in vispy
          alpha : float
              transparency (0 = transparent, 1 = opaque)
          colorbar : bool
              add a colorbar at the back of the surface