Change the color of QRubberBand

[franco.amato]

Hi to all I need to select a region over my waveform display so someone suggested to me to use QRubberBand. I tried it and it works but I would change the selection color to transparent red so I found in internet this class

class WfRubberBand : public QRubberBand
{
public:
 
	WfRubberBand( Shape s, QWidget * p = 0 ) : QRubberBand( s, p ) 
	{
		QPalette palette;
		//palette.setBrush( QPalette::WindowText, QBrush( Qt::red ) );
		palette.setBrush( QPalette::Foreground, QBrush( Qt::red ) );
		setPalette(palette);
	}
 
protected:
 
	virtual void paintEvent( QPaintEvent * ) 
	{
		QStylePainter painter(this);
 
		QStyleOptionFocusRect option;
		option.initFrom( this );
 
		painter.drawControl(QStyle::CE_FocusFrame, option);
	}
};

class WfRubberBand : public QRubberBand
{
public:

	WfRubberBand( Shape s, QWidget * p = 0 ) : QRubberBand( s, p ) 
	{
		QPalette palette;
		//palette.setBrush( QPalette::WindowText, QBrush( Qt::red ) );
		palette.setBrush( QPalette::Foreground, QBrush( Qt::red ) );
		setPalette(palette);
	}

protected:

	virtual void paintEvent( QPaintEvent * ) 
	{
		QStylePainter painter(this);

		QStyleOptionFocusRect option;
		option.initFrom( this );

		painter.drawControl(QStyle::CE_FocusFrame, option);
	}
};

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I tested it and effectively it draw a red rectangle but filled and not transparent so I added this line

setWindowOpacity( 0.0 );

setWindowOpacity( 0.0 );

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without any effects.

How can I do to have a transparency?
May be should I use composition instead of rubberband?
Best Regards,
Franco