#include <QtGui>

class MyDialog : public QDialog
{
   Q_OBJECT
public:
    MyDialog(QWidget *parent = 0) : QDialog(parent), isRed(false)
    {
        b1 = new QPushButton("b1");
        //b1->setAttribute(Qt::WA_NativeWindow, false);
        b2 = new QPushButton("b2");
        b3 = new QPushButton("b3");
        QVBoxLayout *vl = new QVBoxLayout(this);
        vl->addWidget(b1);
        vl->addWidget(b2);
        vl->addWidget(b3);

        int siz = 25;
        b3->setFixedHeight(siz);
        b3->setFixedWidth(siz);

        connect(b1, SIGNAL(clicked()), this, SLOT(changeColor()));
        connect(b2, SIGNAL(clicked()), this, SLOT(changeColor()));
        connect(b3, SIGNAL(clicked()), this, SLOT(changeColor()));
    }

protected slots:
    void changeColor()
    {
        if (!isRed)
            setStyleSheet("QDialog {background-color:red;}");
        else
            setStyleSheet("QDialog {background-color:blue;}");
        isRed = !isRed;
    }

private:
    QPushButton *b1, *b2, *b3;
    int isRed;
};

#include "main.moc"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MyDialog w;
    w.show();
    return a.exec();
}