Format label
        If value is missing, label will be colored red

def get_label(self, prop, value):
        """
        Format label
        If value is missing, label will be colored red
        """
        if value is None:
            return '{}: <FONT color="red">{}</FONT>'.format(prop, "not set")
        else:
            return "{}:{}".format(prop, value)