UIPopoverPresentationController dimming background darker

Since the user is asking for an Obj C solution - use in the VC that's being displayed in the popover

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
    self.popoverPresentationController.containerView.backgroundColor = [[UIColor blackColor] colorWithAlphaComponent:0.4];
}

Swift 4

I just came upon the same problem and found a solution similar to jimmyjudas.

In the viewController displayed as a popover:

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        self.presentingViewController?.view.alpha = 0.3
    }

    override func viewWillDisappear(_ animated: Bool) {
        super.viewWillDisappear(animated)
        self.presentingViewController?.view.alpha = 1
    }

Easiest method is to simply call self.view.alpha = 0.2 before presenting the popover and setting it back to 1.0 when the popover is dismissed.