navigation bar 배경색상 조절

let nav = self.navigationController?.navigationBar  nav?.barTintColor = UIColor(red: 237.0/255.0, green: 237.0/255.0, blue: 242.0/255.0, alpha: 1.0)  nav?.tintColor = UIColor(red: 0/255.0, green: 123.0/255.0, blue: 255.0/255.0, alpha: 1.0)  nav?.titleTextAttributes = [NSForegroundColorAttributeName: UIColor.blackColor()]