仅更改一个UITabBarItem的背景色

class CustomTabBarController: UITabBarController {
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 更改UITabBarItem的背景色
        let selectedColor = UIColor.red
        let unselectedColor = UIColor.gray
        
        UITabBar.appearance().tintColor = selectedColor
        UITabBar.appearance().unselectedItemTintColor = unselectedColor
    }
}

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
    // 创建自定义的UITabBarController
    let customTabBarController = CustomTabBarController()
    
    // 设置为根视图控制器
    window?.rootViewController = customTabBarController
    window?.makeKeyAndVisible()
    
    return true
}