It seems there is something wrong here and it's creating another problem.

Qt Code: 
  1. void DragWidget::mousePressEvent(QMouseEvent *event)
  2. {
  3.  
  4.     // Pack mime data
  5.     QMimeData *mimeData = new QMimeData;
  6.     mimeData->setColorData(QVariant(myColor));
  7.  
  8.     // Prepare cursor image
  9.     QPixmap pixmap(this->size());
  10.     QPainter painter;
  11.     painter.begin(&pixmap);
  12.     painter.fillRect(pixmap.rect(), myColor);
  13.     painter.end();
  14.  
  15.     // We establish QDrag object, draw cursor and embed data
  16.     QDrag *drag = new QDrag(this);
  17.     drag->setMimeData(mimeData);
  18.     drag->setPixmap(pixmap);
  19.     drag->setHotSpot(event->pos());
  20.  
  21.     sourcePicker = drag->source();
  22.  
  23.     // We send it
  24.    drag->exec(Qt::CopyAction);
  25.  
  26.  
  27. }
  28.  
  29. void DragWidget::mouseReleaseEvent(QMouseEvent *event)
  30. {
  31.  
  32.     if (event->type() == QEvent::MouseButtonRelease){
  33.         QColor color = QColorDialog::getColor(QColor(myColor), this);
  34.          if (color.isValid()) {
  35.              setPalette(QPalette(color));
  36.              setAutoFillBackground(true);
  37.              myColor = color;
  38.          }
  39.      }
  40.     else
  41.         event->ignore();
  42. }
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With this line in "mousePressEvent":
Qt Code: 
  1. drag->exec(Qt::CopyAction);
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drag n drop is working fine but "mouseReleaseEvent" is not getting called. If I comment this
line "releaseEvent" is getting called.

Secondly, I have to add the functionality to make this widget as color picker also, I added color picking dialog in "releaseEvent". This won't work as expected because the "dropping"
event is actually a "releaseEvent" and as you drop on target picker dialog shows up.

A hack to this problem is to show color dialog when there is "down" and "up" on same widget. Using a bool var, you set state true, when there is a mouse down and in mouse up
event, check the state of this var, if it's true, show color dialog and set it again to false.
Am I right here or there is a better way of doing this?

How do I setup a menu, which appears at dropping? "swap color" or "replace color"

Prashant