I have been able to make it work by subclassing a UITabBarController and using private classes:
@interface UITabBarController (private)
- (UITabBar *)tabBar;
@end
@implementation CustomUITabBarController
- (void)viewDidLoad {
[super viewDidLoad];
CGRect frame = CGRectMake(0.0, 0.0, self.view.bounds.size.width, 48);
UIView *v = [[UIView alloc] initWithFrame:frame];
[v setBackgroundColor:kMainColor];
[v setAlpha:0.5];
[[self tabBar] addSubview:v];
[v release];
}
@end