code: def _change_color(self, event):
          
          h = self.bar.get()
          self.square.set_hue(h)
          (r, g, b), (h, s, v), sel_color = self.square.get()
          self.red.set(r)
          self.green.set(g)
          self.blue.set(b)
          self.hue.set(h)
          self.saturation.set(s)
          self.value.set(v)
          self.hexa.delete(0, "end")
          self.hexa.insert(0, sel_color.upper())
          if self.alpha_channel:
              self.alphabar.set_color((r, g, b))
              self.hexa.insert('end',
                               ("%2.2x" % self.alpha.get()).upper())
          self._update_preview()
docs: Respond to motion of the hsv cursor.