QTreeWidgetItem color

I am using the following stylesheet on a QTreeWidget to change the items style:

QTreeWidget::item
{
    padding-left:10px;
    padding-top: 1px;
    padding-bottom: 1px;
    border-left: 10px;
}

After that, I am trying to use the following code to change the color of some specific cells:

// item is a QTreeWidgetItem
item->setBackgroundColor(1, QColor(255, 129, 123));

But the color is not changing. I then discovered that, if I remove the stylesheet from the QTreeWidget, then the color change works.

Any idea how to make the background color change to work keeping the stylesheet?

Use a custom delegate to paint your items instead of stylesheets.

Reimplement the paint() method to control the way how are the items drawn:

class CMyDelegate : public QStyledItemDelegate
{
public:
    CMyDelegate(QObject* parent) : QStyledItemDelegate(parent) {}

    void CMyDelegate::paint(QPainter* painter, const QStyleOptionViewItem & option, const QModelIndex & index) const override;
}

void CMyDelegate::paint(QPainter* painter, const QStyleOptionViewItem & option, const QModelIndex & index) const
{
    QStyleOptionViewItemV4 itemOption(option)
    initStyleOption(&itemOption, index);

    itemOption.rect.adjust(-10, 0, 0, 0);  // Make the item rectangle 10 pixels smaller from the left side.

    // Draw your item content.
    QApplication::style()->drawControl(QStyle::CE_ItemViewItem, &itemOption, painter, nullptr);

    // And now you can draw a bottom border.
    painter->setPen(Qt::black);
    painter->drawLine(itemOption.rect.bottomLeft(), itemOption.rect.bottomRight());
}

And this is how to use your delegate:

CMyDelegate* delegate = new CMyDelegate(tree);
tree->setItemDelegate(delegate);

More documentation here: http://doc.qt.io/qt-5/model-view-programming.html#delegate-classes