De Ray Wenderlich:
http://www.raywenderlich.com/4344/user-interface-customization-in-ios-5
// Customize the title text for *all* UINavigationBars
[[UINavigationBar appearance] setTitleTextAttributes:
[NSDictionary dictionaryWithObjectsAndKeys:
[UIColor colorWithRed:255.0/255.0 green:255.0/255.0 blue:255.0/255.0 alpha:1.0],
UITextAttributeTextColor,
[UIColor colorWithRed:0.0 green:0.0 blue:0.0 alpha:0.8],
UITextAttributeTextShadowColor,
[NSValue valueWithUIOffset:UIOffsetMake(0, -1)],
UITextAttributeTextShadowOffset,
[UIFont fontWithName:@"Arial-Bold" size:0.0],
UITextAttributeFont,
nil]];
Ou se preferir com o estilo literal do objeto:
[[UINavigationBar appearance] setTitleTextAttributes:@{
UITextAttributeTextColor: [UIColor colorWithRed:255.0/255.0 green:255.0/255.0 blue:255.0/255.0 alpha:1.0],
UITextAttributeTextShadowColor: [UIColor colorWithRed:0.0 green:0.0 blue:0.0 alpha:0.8],
UITextAttributeTextShadowOffset: [NSValue valueWithUIOffset:UIOffsetMake(0, -1)],
UITextAttributeFont: [UIFont fontWithName:@"Arial-Bold" size:0.0],
}];
Editar para iOS 7 e seguintes
UITextAttributes estão obsoletos como iOS 7, você pode usar o seguinte:
NSShadow *shadow = [[NSShadow alloc] init];
shadow.shadowColor = [UIColor colorWithWhite:.0f alpha:1.f];
shadow.shadowOffset = CGSizeMake(0, -1);
[[UINavigationBar appearance] setTitleTextAttributes:@{
NSForegroundColorAttributeName: [UIColor whiteColor],
NSShadowAttributeName: shadow,
NSFontAttributeName: [UIFont fontWithName:@"Arial-Bold" size:15.0f]
}];