def METHOD_NAME(self):
    """Receive layer model color_by change event and update combobox."""
    with self.layer.events.color_by.blocker():
        color_by = self.layer.color_by
        idx = self.color_by_combobox.findText(
            color_by, Qt.MatchFlag.MatchFixedString
        )
        self.color_by_combobox.setCurrentIndex(idx)