You can set the bar tint color using the barTintColor property:
[[UINavigationBar appearance] setBarTintColor:[UIColor purpleColor]];
If you also don't want the navigation bar to be translucent, you can set the translucent property to NO.
Unfortunately, the translucent property is not available on the UINavigationBar appearance proxy, so you will have to set this property individually (in your storyboard, .xib, or in something like viewDidLoad in your controller).