private void rect_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
    {
        Rectangle r = (Rectangle)sender;
        DataObject dataObj = new DataObject(r.Fill);
        DragDrop.DoDragDrop(r, dataObj, DragDropEffects.Move);
    }

    private void Spadnuti_Drop(object sender, DragEventArgs e)
    {
        SolidColorBrush scb = (SolidColorBrush)e.Data.GetData(typeof(SolidColorBrush));
        Spadnuti.Fill = scb;
    }