class MyProgressBar(QtGui.QProgressBar):
    def setValue(self, value):
        QtGui.QProgressBar.setValue(self, value)
        if value == self.maximum():
            palette = QtGui.QPalette(self.palette())
            palette.setColor(QtGui.QPalette.Highlight, 
                             QtGui.QColor(QtCore.Qt.red))
            self.setPalette(palette)