Change color of translucent black UINavigationBar

Once you know it, it’s fairly simple:

self.navigationController.navigationBar.tintColor = [UIColor blueColor];
self.navigationController.navigationBar.alpha = 0.7f;
self.navigationController.navigationBar.translucent = YES;

The translucent property seems only to determine wether the main view should be visible under the navigation bar, and resizes the view appropiately.