Remove pale-effect on NSStatusBarButton - swift

Question

I'm looking for a way to remove the pale effect from the NSStatusBarButton. This is a picture of how it currently looks:
This is how it should look:
After looking at Apple's documentation, I found a solution to the problem. If you set the appearance of the button directly (e.g. Aqua or DarkAqua), the pale effect disappears:
if let button = statusBarItem.button {
...
button.appearance = NSAppearance.current // or aqua / darkAqua
}
But the problem is when the user changes the interface theme (e.g. from dark mode to light mode), the NSStatusBarButton does not change its appearance automatically:
I could monitor AppleInterfaceThemeChangedNotification and then change the appearance, but that's not a clean solution and I'm not happy with it.
Is there an elegant solution to this? The image in the NSStatusBarButton should simply be displayed without changes (e.g. pale). Because I offer all flags of the world, I only have the images in png format, no PDF images.

Answer 1

Since the solution of vadian, unfortunately, did not work for me, I would like to show my alternative solution here. Maybe it helps somebody else.
Create the NSStatusItem and customize NSStatusBarButton:
...
if let button = statusBarItem.button {
...
button.appearance = NSAppearance.current // removes the pale effect
}
...
Write an extension for Notification.Name to react on AppleInterfaceThemeChangedNotification:
extension Notification.Name {
static let AppleInterfaceThemeChangedNotification = Notification.Name("AppleInterfaceThemeChangedNotification")
}
Add an Observer to the new notification name:
DistributedNotificationCenter.default.addObserver(self, selector: #selector(interfaceChanged), name: .AppleInterfaceThemeChangedNotification, object: nil)
Respond to the change between light/dark mode:
#objc private static func interfaceChanged() {
// change button.appearance
}
Make sure that button.appearance is only changed if the necessary macOS version is available:
guard #available(OSX 10.14, *) else {
return
}
I am sure that there is a cleaner solution. If anyone has an idea, please tell me.

Answer 2

Write an extension of NSStatusBarButton and override viewDidChangeEffectiveAppearance.
In the body of the method change the appearance explicitly
extension NSStatusBarButton {
#available(macOS 10.14, *)
override public func viewDidChangeEffectiveAppearance() {
print("viewDidChangeEffectiveAppearance")
self.appearance = .current
}
}