SwiftでUITabBarControllerの選択色をタブごとに変える

MyTabBarController
   -> UINavigationController -> MyNavigationControllerA
   -> UINavigationController -> MyNavigationControllerB
   -> UINavigationController -> MyNavigationControllerC

func tabBarController(tabBarController: UITabBarController, shouldSelectViewController viewController: UIViewController) -> Bool {
    guard let tabContent = viewController as? UINavigationController else {
        return true
    }
    let navigationContent = tabContent.viewControllers[0]
    if nil != navigationContent as? MyNavigationControllerB {
        // Bの時だけ選択色を赤に
        tabBar.tintColor = UIColor(red: 1.0, green: 0.0, blue: 0.0, alpha: 1.0)
    } else {
        // それ以外は緑に
        tabBar.tintColor = UIColor(red: 0.0, green: 1.0, blue: 0.0, alpha: 1.0)
    }
    return true
}