在UIImagePickerControllerDelegate方法中编写：
- (void)navigationController:(UINavigationController *)navigationController didShowViewController:(UIViewController *)viewController animated:(BOOL)animated {
UINavigationBar *navigationBar = navigationController.navigationBar;
[navigationBar setBackgroundImage:[UIImage imageNamed:@"background.png"] forBarMetrics:UIBarMetricsDefault];
navigationBar.tintColor = [UIColor whiteColor];
[[UINavigationBar appearance] setTitleTextAttributes:@{NSForegroundColorAttributeName:[UIColor whiteColor]}];
}
