code: def _update_alpha(self, event=None):
          
          a = self.alpha.get()
          hexa = self.hexa.get()
          hexa = hexa[:7] + ("%2.2x" % a).upper()
          self.hexa.delete(0, 'end')
          self.hexa.insert(0, hexa)
          self.alphabar.set(a)
          self._update_preview()
docs: Update display after a change in the alpha spinbox.