qt change background color

    QPalette palette;
    palette.setBrush(this->backgroundRole(),QBrush(QColor(128,128,128)));
    palette.setColor(QPalette::Button, QColor(128,128,128));
    palette.setColor(QPalette::WindowText, QColor(230, 230, 230));

    this->setPalette(palette);
    this->setAutoFillBackground(true);