<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def disable(self):
 """ Disable the button, if in non-expert mode. """

        w.ActButton.disable(self)
        g = get_root(self).globals
        if self._expert:
            self.config(bg=g.COL['start'])
        else:
            self.config(bg=g.COL['startD'])