 extension UIColor
 {
     fileprivate struct AssociatedKeys
-    {
-        static var defNavBarBarTintColor: UIColor = UIColor.white // UIColor.init(red: 0/255.0, green: 175/255.0, blue: 240/255.0, alpha: 1)
-        static var defNavBarTintColor: UIColor = UIColor.white
+    {   // default is system attributes
+        static var defNavBarBarTintColor: UIColor = UIColor.white
+        static var defNavBarTintColor: UIColor = UIColor(red: 0, green: 0.478431, blue: 1, alpha: 1.0)
         static var defStatusBarStyle: UIStatusBarStyle = UIStatusBarStyle.default
     }
     class var defaultNavBarBarTintColor: UIColor {

            {
                // 这里如果不做判断的话，会显示 backIndicatorImage(系统返回按钮)
                if let _UINavigationBarBackIndicatorViewClass = NSClassFromString("_UINavigationBarBackIndicatorView"),
                   let _UIBarBackgroundClass                  = NSClassFromString("_UIBarBackground")
                {
                    if (view.isKind(of: _UINavigationBarBackIndicatorViewClass) == false && view.isKind(of: _UIBarBackgroundClass) == false) {
                        view.alpha = alpha
                    }
                }
            }

        navigationBar.wr_setBackgroundColor(color: barTintColor)
    }
    
    fileprivate func setNeedsNavigationBarUpdate(barBackgroundAlpha: CGFloat)
    {
        navigationBar.wr_setBackgroundAlpha(alpha: barBackgroundAlpha)
    }
    
    fileprivate func setNeedsNavigationBarUpdate(tintColor: UIColor) {
