一、如果只是設置選中狀態的字體顏色，使用 tintColor  就可以達到效果

self.tabBar.tintColor = [UIColor redColor];二、但如果要將未選中狀態和選中狀態下的顏色都改變，可以使用 setTitleTextAttributes:<#(nullable NSDictionary<NSString *,id> *)#> forState:<#(UIControlState)#> 達到效果
[nav.tabBarItem setTitleTextAttributes:@{NSForegroundColorAttributeName:[UIColor redColor]} forState:UIControlStateNormal];[nav.tabBarItem setTitleTextAttributes:@{NSForegroundColorAttributeName:[UIColor blueColor]} forState:UIControlStateSelected];       或者
[[UITabBarItem appearance] setTitleTextAttributes:@{NSForegroundColorAttributeName:[UIColor redColor]} forState:UIControlStateNormal];[[UITabBarItem appearance] setTitleTextAttributes:@{NSForegroundColorAttributeName:[UIColor blueColor]} forState:UIControlStateSelected];