def white(self, group=None):
        """ Switch lights on and change color to white.
            If group (1-4) is not specified, all four groups
            will be switched on and to white. """
        if group is None or group == 0:
            self._send_to_group(group, command="all_white")
            return
        self._send_to_group(group, per_group=True, rgbw_cmd=self.RGBW_GROUP_X_TO_WHITE)