导航栏返回键
UINavigationBar *navBar = [UINavigationBar appearance];
navBar.tintColor = [UIColor whiteColor]; //可以修改导航栏 返回箭头的颜色
http://www.cocoachina.com/ask/questions/show/87783
[self.navigationController.navigationBar setTitleTextAttributes: @{NSFontAttributeName:[UIFont systemFontOfSize:19],NSForegroundColorAttributeName:[UIColor redColor]}];
IOS6、IOS7导航栏适配问题
http://www.itstrike.cn/Question/e0fd5e29-34ef-49fe-9a55-a018878199a2.html