How can I change the backBarButtonItem colour in Swift?

I am trying to change the default backBarButtonItem colour to white colour,

my codes look like below

self.navigationItem.backBarButtonItem?.tintColor = UIColor.whiteColor()

But It is not working for me, any ideas?

If you want to change the backBarButton do this :

override func viewDidLoad() {

    super.viewDidLoad()

    let newBackButton = UIBarButtonItem(title: "B",
    style: UIBarButtonItem.Style.plain, target: self, action: "backAction")
        navigationController?.navigationBar.topItem?.backBarButtonItem = newBackButton
    newBackButton.tintColor = .red
    // Do any additional setup after loading the view.
}

func backAction() -> Void {
    self.navigationController?.popViewController(animated: true)
}

image of code

See the result: