QtQuick colour palette for disabled widgets

I am working on a Qt (QML) application that requires darker color palette. Based on some examples I created a qtquickcontrols2.conf file with the following content:

[Controls]
Style=Fusion

[Fusion\Palette]
AlternateBase=#353535
Base=#191919
BrightText=red
Button=#353535
ButtonText=white
Highlight=#2a82da
HighlightedText=gray
Link=#2a82da
Text=white
ToolTipBase=white
ToolTipText=white
Window=#353535
WindowText=#dddddd

The colour palette works just fine for active mode of widgets. However, disabled widgets look exactly the same as active ones. I did not find a way to add colours for disabled widgets to the config file. It seems that it can't be done.

Then I had an idea to create lighter version of active palette in application main.

QPalette& updateDisabledColors(QPalette &palette)
{
    palette.setColor(QPalette::Disabled, QPalette::Window, palette.window().color().lighter());
    palette.setColor(QPalette::Disabled, QPalette::WindowText, palette.windowText().color().lighter());
    palette.setColor(QPalette::Disabled, QPalette::Base, palette.base().color().lighter());
    palette.setColor(QPalette::Disabled, QPalette::AlternateBase, palette.alternateBase().color().lighter());
    palette.setColor(QPalette::Disabled, QPalette::Text, palette.text().color().lighter());
    palette.setColor(QPalette::Disabled, QPalette::Button, palette.button().color().lighter());
    palette.setColor(QPalette::Disabled, QPalette::ButtonText, palette.buttonText().color().lighter());
    palette.setColor(QPalette::Disabled, QPalette::BrightText, palette.brightText().color().lighter());
    palette.setColor(QPalette::Disabled, QPalette::Link, palette.link().color().lighter());
    palette.setColor(QPalette::Disabled, QPalette::Highlight, palette.highlight().color().lighter());
    palette.setColor(QPalette::Disabled, QPalette::HighlightedText, palette.highlightedText().color().lighter());

    return palette;
}


int main(int argc, char *argv[])
{
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);

    QApplication app(argc, argv);

// Tried to change palette here also

    QQmlApplicationEngine engine;

    engine.load(QUrl(QStringLiteral("qrc:/qml/main.qml")));
    if (engine.rootObjects().isEmpty()) {
        return -1;
    }

    auto palette = app.palette();
    palette = updateDisabledColors(palette);
    app.setPalette(palette);

    return app.exec();
}

The palette acquired from the app is not the one defined in qtquickcontrol2.conf.

What is the proper way to modify palette colours for disabled widgets when using QML?

As far as I can tell, setting the Fusion style Palette in qtquickcontrols2.conf does not update the default Q[Gui]Application palette. But the opposite works -- the default Controls2 palette is the system-wide default QPalette which can be set with Q[Gui]Application::setPalette(). So you could set all the color groups in C++ code, like you do now for just the Disabled group.

Looking at the relevant code, it also looks like you can specify a Disabled subgroup in qtquickcontrols2.conf (e.g. Fusion/Palette/Disabled). I'm not sure which versions of Qt this is available in, nor do I see this documented anywhere.

ADDED: Looks like the Palette and subgroups are read from conf file since at least Qt 5.10 (which is also when the Control::palette property was introduced).