Window colour

[phillip_Qt]

HI all.
I ve changed the colour of window by usning the code

QPalette p( this->palette());
p.setColor( QPalette::Window, QColor(Qt::black));
this->setPalette(p);

QPalette p( this->palette());
p.setColor( QPalette::Window, QColor(Qt::black));
this->setPalette(p);

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now i need to check the window colour. if it is black i need 2 change it to gray and vice versa. i Tried to do as below but its not working

if(QMainWindow::backgroundRole() == Qt::black)
{
    QPalette p( this->palette());
   p.setColor( QPalette::Window, QColor(Qt::gray));
   this->setPalette(p);
}

if(QMainWindow::backgroundRole() == Qt::black)
{
    QPalette p( this->palette());
   p.setColor( QPalette::Window, QColor(Qt::gray));
   this->setPalette(p);
}

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But its not coming inside if loop.
Can any body help me.
thank you all.