So as I stated in https://github.com/olive-editor/olive/issues/545#issuecomment-466642704, on Windows it would look way more professional to let the menu bar use the systems style (just like as Premiere does). Fusion is great, I like it really much, but using it anywhere gives the application in my opinion (on windows) a more clumsy look.
I wrote a sample application and set it up in theming just like Olive.
qApp->setStyle(QStyleFactory::create("Fusion"));
QPalette darkPalette;
darkPalette.setColor(QPalette::Window, QColor(53,53,53));
darkPalette.setColor(QPalette::WindowText, Qt::white);
darkPalette.setColor(QPalette::Base, QColor(25,25,25));
darkPalette.setColor(QPalette::AlternateBase, QColor(53,53,53));
darkPalette.setColor(QPalette::ToolTipBase, QColor(25,25,25));
darkPalette.setColor(QPalette::ToolTipText, Qt::white);
darkPalette.setColor(QPalette::Text, Qt::white);
darkPalette.setColor(QPalette::Button, QColor(53,53,53));
darkPalette.setColor(QPalette::ButtonText, Qt::white);
darkPalette.setColor(QPalette::BrightText, Qt::red);
darkPalette.setColor(QPalette::Disabled, QPalette::ButtonText, QColor(128, 128, 128));
darkPalette.setColor(QPalette::Link, QColor(42, 130, 218));
darkPalette.setColor(QPalette::Highlight, QColor(42, 130, 218));
darkPalette.setColor(QPalette::HighlightedText, Qt::black);
qApp->setPalette(darkPalette);
QMenuBar *menuBar = new QMenuBar(this);
menuBar->setStyle(QStyleFactory::create("windowsvista"));
menuBar->setStyleSheet("color: black;");
QList<QMenu*> menuList;
fileMenu = menuBar->addMenu("File");
helpMenu = menuBar->addMenu("Edit");
menuList.append(fileMenu);
menuList.append(helpMenu);
Q_FOREACH(QMenu *m, menuList) {
m->setStyle(QStyleFactory::create("windowsvista"));
}
this->setMenuBar(menuBar);
What I achieve is this: 
The problem is as you can see I currently set the colors of the menubar manually using the setStyleSheet option. Any ideas about that? Shouldn't be an option to do this using this way. Even though this should also be done in the Q_FOREACH because the QPalette is also overriding the actual color of the menu bar's items.
Also is this a way to go? I would like it much more with that style on that platform...
"More professional" is very subjective, but I can appreciate the appeal of getting a more native experience. I did actually briefly experiment with this a while back and found the same thing you did - it requires "un-setting" the style on all QMenu objects individually. There may be a trick to make it simpler (e.g. subclassing QMenu to always set itself to windowsvista on Windows), but unfortunately I don't think there's anything as clean as setting a style on just the whole class or something.
Atleast we could give the user the ability to set a checkbox in preferences for that (if we're on windows). I'll test around a little bit in the next days...
Indeed, if this can be implemented cleanly, I'll make it default on Windows probably with an option somewhere to revert to full Fusion.
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