Qt: Set isMask to true on menu items

Prevents icons from being the wrong color when the Qt theme doesn't match the macOS system theme (or when you use Native theme with dark mode)

pcsx2-qt/MainWindow.cpp

@@ -64,7 +64,11 @@ static constexpr char DISC_IMAGE_FILTER[] =
 									"GS Dumps (*.gs *.gs.xz *.gs.zst);;"
 									"Block Dumps (*.dump)");
 
+#ifdef __APPLE__
+const char* MainWindow::DEFAULT_THEME_NAME = "";
+#else
 const char* MainWindow::DEFAULT_THEME_NAME = "darkfusion";
+#endif
 
 MainWindow* g_main_window = nullptr;
 
@@ -97,8 +101,30 @@ void MainWindow::initialize()
 	updateSaveStateMenus(QString(), QString(), 0);
 }
 
+// TODO: Figure out how to set this in the .ui file
+/// Marks the icons for all actions in the given menu as mask icons
+/// This means macOS's menubar renderer will ignore color values and use only the alpha in the image.
+/// The color value will instead be taken from the system theme.
+/// Since the menubar follows the OS's dark/light mode and not our current theme's, this prevents problems where a theme mismatch puts white icons in light mode or dark icons in dark mode.
+static void makeIconsMasks(QWidget* menu)
+{
+	for (QAction* action : menu->actions())
+	{
+		if (!action->icon().isNull())
+		{
+			QIcon icon = action->icon();
+			icon.setIsMask(true);
+			action->setIcon(icon);
+		}
+		if (action->menu())
+			makeIconsMasks(action->menu());
+	}
+}
+
 void MainWindow::setupAdditionalUi()
 {
+	makeIconsMasks(menuBar());
+
 	const bool toolbar_visible = Host::GetBaseBoolSettingValue("UI", "ShowToolbar", false);
 	m_ui.actionViewToolbar->setChecked(toolbar_visible);
 	m_ui.toolBar->setVisible(toolbar_visible);