UIDocumentPickerViewController - How to set the navigation bar color

I want to set the navigation bar background color of my DocumentPicker to be the same as the rest of my application.

    let filePicker = UIDocumentPickerViewController(documentTypes: ["public.content"], in: .import)
    filePicker.delegate = self
    filePicker.navigationController?.navigationBar.barTintColor = self.theme.navigationBarColor

    self.present(filePicker, animated: true, completion: nil)

doesn't work.

Other things I've tried:

Use UINavigationBar.appearance().backgroundColor = self.theme.navigationBarColor - doesn't work and looks too much like a workaround instead of a proper way if it works.

Edit: Right now our app is redesigned to use the primary color as navigation bar text color, and have the same background color as the DocumentPicker. Answers will still be appreciated.