PoEdit comes the closest to looking genuinely native, but the MacOS implementation is clearly flawed.
Or check "Game Develop". The primary interface is a kind of weird rip-off of the MS Office ribbon, but I assume this is a custom widget. There's also a tab interface though, and this doesn't work on either the Windows or GTK versions: it's weird and has a gradient background.
In general, small details like the padding, coloration, and borders drawn around widgets seem to be slightly off on most platforms with just about very wx based GUI I've seen.
The rest of the controls (ribbon, tabs) are indeed non-native and there are no native equivalents for them, so there is not much to say here.
Generally speaking, there shouldn't be any problem with the colours unless you change them explicitly, which is a bad idea for the native controls. Not sure what is wrong with the padding and borders.
Well, let's verify that… https://i.imgur.com/uHfjoUs.png No, they're not.
> draggable/dockable tabs/panels […] You can't say they differ from native ones because there is just no native version
That sounds wrong. Why should they not be? Do you have any proof?
Sorry, I don't know what is this supposed to prove, but I can definitely assure you that all the mentioned controls, and many others, are exactly native controls under the 3 first tier platforms (MSW, GTK and macOS).
> Do you have any proof?
Proof of absence of something is hard to make, all I can say is that you can go through MSDN, GTK and Cocoa documentation to convince yourself.
It does for the widgets that have no native equivalent, such as draggable/dockable tabs/panels that you show. You can't say they differ from native ones because there is just no native version, on any platform.
OTOH all the standard UI elements (buttons, checkboxes, text controls, date pickers, ...) are native and not only they look natively, but also behave natively, which is pretty important and different from Qt.