Qt QcolorDialog - Ok button don't work

Question

I'm use window qt, this is my code:

LaserEllipse::LaserEllipse(QWidget *parent):
                .....
        QLabel(parent),
        _colore(new QColorDialog(this))
{
    ......
    _colore->setCurrentColor(....);


    // COSTRUZIONE MENU     
    _action_remove = new QAction("Remove Item" , this );
    _action_color = new QAction("Change color" , this );    

    _contextMenu->addAction(_action_color);
    _contextMenu->addAction(_action_remove);

    connect(_action_remove, SIGNAL(triggered()), this, SLOT(action_remove()));
    connect(_action_color, SIGNAL(triggered()), this, SLOT(action_color()));

    _contextMenu->setStyleSheet("QMenu{background-color: rgba(255,255,255,255);selection-color: black;selection-background-color: rgba(162,217,247);}");
    _colore->setStyleSheet("background-color: rgba(255,255,255,255);");
};



void LaserEllipse::action_color()   
{   
    _colore->open(this, SLOT(aggiornaEllipse()));   
}

void LaserEllipse::aggiornaEllipse()
{
    _ellipse_t->setColor(_colore->currentColor().toRgb().name().toStdString());
    _ellipse_t->setCX(this->geometry().center().x()); 
    _ellipse_t->setCY(this->geometry().center().y()); 
    _ellipse_t->setRX(this->width() / 2);
    _ellipse_t->setRY(this->height() / 2);  
}

In the last line, in action_color slot function, appear QColorDialog, but if I click "Ok" the button keep pressed down and don't work, if I click "Cancel" nothing happens. To change color I must press enter.

What is wrong ?