iOS 11 customise search bar in navigation bar

Put

UITextField.appearance(whenContainedInInstancesOf: [UISearchBar.self]).defaultTextAttributes = [NSForegroundColorAttributeName: UIColor.white]

and

UISearchBar.appearance().tintColor = UIColor.white in the AppDelegate.

Alternatively, put them both in [UIViewController viewDidLoad:]

I just found out how to set also the rest of them: (with some help of Brandon, thanks!)

The "Cancel" text:

searchController.searchBar.tintColor = .white

The search icon:

searchController.searchBar.setImage(UIImage(named: "my_search_icon"), for: UISearchBarIcon.search, state: .normal)

The clear icon:

searchController.searchBar.setImage(UIImage(named: "my_search_icon"), for: UISearchBarIcon.clear, state: .normal)

The search text:

UITextField.appearance(whenContainedInInstancesOf: [UISearchBar.self]).defaultTextAttributes = [NSAttributedStringKey.foregroundColor.rawValue: UIColor.white]

Thanks for the help @Brandon!

The placeholder:

UITextField.appearance(whenContainedInInstancesOf: [UISearchBar.self]).attributedPlaceholder = NSAttributedString(string: "placeholder", attributes: [NSAttributedStringKey.foregroundColor: UIColor.white])

The white background:

let searchController = UISearchController(searchResultsController: nil)
searchController.delegate = self

let searchBar = searchController.searchBar
searchBar.tintColor = UIColor.white
searchBar.barTintColor = UIColor.white

if let textfield = searchBar.value(forKey: "searchField") as? UITextField {
    textfield.textColor = UIColor.blue
    if let backgroundview = textfield.subviews.first {

        // Background color
        backgroundview.backgroundColor = UIColor.white

        // Rounded corner
        backgroundview.layer.cornerRadius = 10;
        backgroundview.clipsToBounds = true;
    }
}

if let navigationbar = self.navigationController?.navigationBar {
    navigationbar.barTintColor = UIColor.blue
}

navigationItem.searchController = searchController
navigationItem.hidesSearchBarWhenScrolling = false

Taken from here.