How to set unsafe area background color for ios 11

It looks like a hacky trick but you may try this:
You can set background color for status bar during application launch or during viewDidLoad of your view controller. Here it works for me, in following ways.

extension UIApplication {

    var statusBarView: UIView? {
        return value(forKey: "statusBar") as? UIView
    }

}

// Set it from your view controller if you've view controller based statusbar
class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        UIApplication.shared.statusBarView?.backgroundColor = UIColor.green
    }

}

or

// Set upon application launch, if you've application based status bar
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
        UIApplication.shared.statusBarView?.backgroundColor = UIColor.green
        return true
    }
}

Here is result:

You have to apply different constraints. Your background color should extend beyond the safe area all the way to the superview. So your constraints need to be set to the superview for your background color but to the safe area for your ui view (buttons, tableViews and the like)