Well, I've solved in this way:

added the following to the constructor:

Qt Code: 
  1. QPen   pen(QColor("blue"));
  2. 	m_Pixmap = new QPixmap(QSize(180, 20));
  3. 	m_Painter = new QPainter(m_Pixmap);
  4. 	m_Painter->setPen(pen);
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and the mousePressEvent is now:

Qt Code: 
  1. void CListWidget::mousePressEvent(QMouseEvent *event)
  2. {
  3. 	QListWidget::mousePressEvent(event);
  4.  
  5. 	if ( currentItem()->text().isEmpty() )
  6. 	{
  7. 		clearSelection();
  8. 		return;
  9. 	}
  10.  
  11. 	QByteArray itemData;
  12. 	QDataStream dataStream(&itemData, QIODevice::WriteOnly);
  13. 	dataStream << currentItem()->text();
  14.  
  15. 	m_Painter->fillRect(QRect(0, 0, 180, 20), QBrush(QColor("orange"))); // ADDED
  16. 	m_Painter->drawText(QRect(10, 0, 170, 20), currentItem()->text() );  // ADDED
  17.  
  18. 	QMimeData *mimeData = new QMimeData;
  19. 	mimeData->setData("application/x-dnditemdata", itemData);
  20. 	mimeData->setText(currentItem()->text());
  21.  
  22. 	QDrag *drag = new QDrag(this);
  23. 	drag->setPixmap(*m_Pixmap);   // ADDED
  24. 	drag->setMimeData(mimeData);
  25. 	drag->exec(Qt::CopyAction);
  26. }
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