UINavigationBar changes to unexpected colors when scrolling / transitioning

Question

I have a UIView with a transparent title bar, and when the user scrolls, the background slowly fades into white.

func imageFromColor(color: UIColor, size: CGSize) -> UIImage {
    let rect = CGRect(x: 0, y: 0, width: size.width, height: size.height)
    UIGraphicsBeginImageContext(rect.size)
    let context = UIGraphicsGetCurrentContext()

    context!.setFillColor(color.cgColor)
    context!.fill(rect)

    var image = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()

    UIGraphicsBeginImageContext(size)
    image?.draw(in: rect)
    image = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()

    return image!
}

override func viewDidLoad() {
    super.viewDidLoad()

    // remove nav bar bottom border
    navigationController?.navigationBar.shadowImage = UIImage()

    // set nav bar button color
    let image = imageFromColor(color: UIColor(red: 255, green: 255, blue: 255, alpha: 0.0), size: CGSize(width: 1, height: 1))
    navigationController?.navigationBar.setBackgroundImage(image, for: .default)

    navigationController?.navigationBar.tintColor = .white
    navigationController?.navigationBar.titleTextAttributes = [NSForegroundColorAttributeName: UIColor.black.withAlphaComponent(0.0)]

When the user scrolls, I discover where they are in the scroll and updates the navigation bar accordingly.

func scrollViewDidScroll(_ scrollView: UIScrollView) {
    var alpha = (scrollView.contentOffset.y / 200)
    alpha = alpha > 1.0 ? 1.0 : alpha

    if let listName = listName, let navBar = navigationController?.navigationBar {
        let height = listName.frame.maxY - navBar.frame.maxY - 3.0
        if scrollView.contentOffset.y > 0 && scrollView.contentOffset.y >= height, !titleShowing {
            titleShowing = true

            UIView.animate(withDuration: 0.3, delay: 0, options: .curveEaseIn, animations: {
                self.titleLabel?.alpha = 1
                self.titleTopConstraint?.constant = -34.0
                self.titleLabel?.layoutIfNeeded()
            }, completion: nil)
        } else if scrollView.contentOffset.y < height, titleShowing {
            self.titleShowing = false
            self.titleLabel?.alpha = 0

            UIView.animate(withDuration: 0.4, delay: 0, options: .curveEaseIn, animations: {
                self.titleTopConstraint?.constant = 0
                self.titleLabel?.layoutIfNeeded()
            }, completion: nil)
        }
    }

    let image = imageFromColor(color: UIColor(red: 255, green: 255, blue: 255, alpha: alpha), size: CGSize(width: 1, height: 1))
    navigationController?.navigationBar.setBackgroundImage(image, for: .default)

    navigationController?.navigationBar.titleTextAttributes = [NSForegroundColorAttributeName: UIColor.black.withAlphaComponent(alpha)]
}

Everything works fine as long as I scrolled down to the place where the Nav bar will be white, and then tap the item that pushes to the presentation controller, which must again be displayed Nav panel with the same setting in viewDidLoad:

let image = imageFromColor(color: UIColor(red: 255, green: 255, blue: 255, alpha: 0.0), size: CGSize(width: 1, height: 1))
navigationController?.navigationBar.setBackgroundImage(image, for: .default)

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