how to dim background view - ios7

Question

trying to dim background view when I work with custom modal view controller I set background color to grey color with 0.5 opacity:
- (void)rulesTapped:(id)sender
{
RulesVC *rulesVC = [[RulesVC alloc] init];
self.view.backgroundColor = [UIColor colorWithRed:0.3 green:0.3 blue:0.3 alpha:0.5];
rulesVC.modalPresentationStyle = UIModalPresentationCustom;
rulesVC.transitioningDelegate = self;
[self presentViewController:rulesVC animated:YES completion:nil];
}
but when I then try to set it back to whiteColor (or yellow) while dismissing the modal VC, this dimming keeps in place:
- (void) gotItTapped:(id)sender
{
[self.presentingViewController.view setBackgroundColor:[UIColor yellowColor]];
[self dismissViewControllerAnimated:YES completion:nil];
}
Why? And is there way to dim background (and then remove dimming) view without adding another overlaying view but just operating with existing view?

Answer 1

I don't think you can achieve it without adding another element to your UIViewController. I normally insert an UIView which is setHidden:YES and alpha 0.0f and blackColor as backgroundColor. When showing something, I always set it Hidden:NO and animate it to opacity 0.6f.
[UIView animateWithDuration:0.5f animations:^{
[self.view setAlpha:0.6];
}];
This way it appears not immediately and looks much smoother.

Answer 2

I actually needed this to be able to put some other UIView in dim view, and that every click outside this dimview, would dismiss both built-in UIView and dimView. What I've discovered, is that for this the best is to imitate a button which is removed from superview upon click:
self.dimView = [UIButton buttonWithType:UIButtonTypeCustom];
self.dimView.backgroundColor = [[UIColor blackColor] colorWithAlphaComponent:0.2f];
self.dimView.frame = CGRectMake(0,
0,
self.view.frame.size.width,
self.view.frame.size.height);
[self.dimView addTarget:self
action:#selector(removeDimView)
forControlEvents:UIControlEventTouchUpInside];