def current_pointing(self, index):
        """set the color of the currently selected pointing to 'blue'"""
        if self.current is not None:
            for item in self.pointings[self.current]['items']:
                self.itemconfigure(item, outline="black")
        self.current = index
        for item in self.pointings[self.current]['items']:
            self.itemconfigure(item, outline="blue")
set the color of the currently selected pointing to 'blue