code: def rgbmap_cb(self, rgbmap, channel):
          
          if not self.gui_up:
              return
          fitsimage = channel.fitsimage
          if fitsimage != self.fv.getfocus_fitsimage():
              return False
          self.change_cbar(self.fv, channel)
docs: This method is called when the RGBMap is changed.  We update
          the ColorBar to match.