UITabBar 设置字体的颜色（选中状态/正常状态）setTitleTextAttributes

UITabbar有个setTintColor这个方法，可以理解为，高亮的时候，或者点击后的颜色设置。

UITabBarItem有个setTitleTextAttributes的方法，是用来设置字体的颜色。

[[UITabBarItem appearance] setTitleTextAttributes:[NSDictionary dictionaryWithObjectsAndKeys:

[UIColor redColor], NSForegroundColorAttributeName,

nil] forState:UIControlStateNormal];

UIColor *titleHighlightedColor = [UIColor greenColor];

[[UITabBarItem appearance] setTitleTextAttributes:[NSDictionary dictionaryWithObjectsAndKeys:

titleHighlightedColor, NSForegroundColorAttributeName,

nil] forState:UIControlStateSelected];