Different color letters in QComboBox edit field

User selects one of possible entries from drop-down list (already drawn with some letters in other then default color). But this selected entry is displayed without color letters (which is understandable). How can I draw/print this text with my own drawing procedure to color some of letters?
I tried to work with paintEvent(). First I call QComboBox::paintEvent() so it would draw default control. Then I tried to use painter->drawTextItem(). Unfortunately - rect for this operation is different then whole control and my new colorful text didn't covered previous one. I don't want to use hardcoded tweaks and values to match my text and the one draw by default.
Are there other possibilities? Once again - I want to draw selected QComboBox text with my own color rules.

Qt supports in some places a simplified HTML syntax. It's been a while but I am pretty sure that you can colorize items in the drop down. I didn't try it this way, but it should work:
"<font color="blue">Blue</font> to <font color="red">Red</font>" which shoudl give you an item "Blue to Red"

Unfortunately this approach isn't working.

I tried something different. As you may notice - QComboBox::paintEvent() is

Code:

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QStylePainter painter(this);
painter.setPen(palette().color(QPalette::Text));
 
// draw the combobox frame, focusrect and selected etc.
QStyleOptionComboBox opt;
initStyleOption(&opt);
painter.drawComplexControl(QStyle::CC_ComboBox, opt);
 
// draw the icon and text
painter.drawControl(QStyle::CE_ComboBoxLabel, opt);

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For my needs - I only need to rewrite last line reponsible for drawing label/edit field (icon and text). And it worked.

Code:

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void SubstituteSearchResultComboBox::paintEvent(QPaintEvent * event)
{
    int start_pos(0), prev_pos(0);
    QStylePainter painter(this);
    painter.setPen(palette().color(QPalette::Text));
 
    QStyleOptionComboBox opt;
    initStyleOption(&opt);
    painter.drawComplexControl(QStyle::CC_ComboBox, opt);
 
    QStyleOptionComboBox cmb;
    initStyleOption(&cmb);
 
    QString text_;
    QFontMetrics font_metric(font());
 
    QModelIndex index = model()->index(currentIndex(),0);
    QString text = model()->data(index).toString();
    SuccessWord success_word = model()->data(index,Qt::UserRole).value<SuccessWord>();
 
    QPen standard_pen = painter.pen();
    standard_pen.setColor(palette().color(QPalette::WindowText));
    QPen special_pen = painter.pen();
    special_pen.setColor(QColor(Qt::red));
    special_pen.setWidth(special_pen.width()+1);
    QRect rect_ = painter.style()->proxy()->subControlRect(QStyle::CC_ComboBox, &cmb, QStyle::SC_ComboBoxEditField, this);
 
    current_width = rect_.left();
    for(char letter : success_word.matchingLetters)
    {
        start_pos = text.indexOf(letter, prev_pos, Qt::CaseInsensitive);
        if (start_pos<0) break;
 
        text_ = text.mid(prev_pos, start_pos-prev_pos);
        drawItem(&painter, rect_ , text_, font_metric.width(text_), standard_pen, current_width);
        prev_pos = start_pos;
 
        text_ = text.mid(prev_pos, 1);
        drawItem(&painter, rect_ , text_, font_metric.width(text_), special_pen, current_width);
        prev_pos++;
    }
    text_ = text.mid(prev_pos);
    drawItem(&painter, rect_ , text_, font_metric.width(text_)+5, standard_pen, current_width);
}

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