def METHOD_NAME(self):
    """
    Add visual cues when formula is incorrect
    """
    # Don't validate if requested
    if not self.validate: return
    formula_is_valid = False
    formula_is_valid = self.validateConstraint(self.txtConstraint.text())
    if not formula_is_valid:
        self.cmdOK.setEnabled(False)
        self.txtConstraint.setStyleSheet("QLineEdit {background-color: red;}")
    else:
        self.cmdOK.setEnabled(True)
        self.txtConstraint.setStyleSheet("QLineEdit {background-color: white;}")