[KevinH]

Okay I found the place in the Qt Windows specific code that sets the forground and background of the QInputMethodEvents:

It is here:

qtbase/src/plugins/platforms/windows
/qwindowsinputcontext.cpp

The code in question is this routine:

enum StandardFormat {
    PreeditFormat,
    SelectionFormat
};

static inline QTextFormat standardFormat(StandardFormat format)
{
    QTextCharFormat result;
    switch (format) {
    case PreeditFormat:
        result.setUnderlineStyle(QTextCharFormat::DashUnderline);
        break;
    case SelectionFormat: {
        // TODO: Should be that of the widget?
        const QPalette palette = QGuiApplication::palette();
        const QColor background = palette.text().color();
        result.setBackground(QBrush(background));
        result.setForeground(palette.window());
        break;
    }
    }
    return result;
}

But it makes no sense as it inverts the foreground and background colors and even adds an underline style.

What bothers me most is the ToDo comment ...