Why are my UIBarButtonItem buttons getting a background color on some devices?

Question

On some devices, my UIBarButtonItem buttons have a background color. I don't know what is causing this. Here is how it looks on some devices:

It should, and does, look like this, on most devices and in the simulator for all device types:

I do make a lot of changes to appearance but I don't see how any of these settings would cause this problem. Here are my appeance settings:

func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {

    UIApplication.sharedApplication().statusBarStyle = .LightContent
    UINavigationBar.appearance().barStyle = .Black

    UINavigationBar.appearance().barTintColor = UIColor.darkGrayColor()
    UINavigationBar.appearance().tintColor = UIColor.whiteColor()
    UINavigationBar.appearance().titleTextAttributes = [NSForegroundColorAttributeName: UIColor.whiteColor()]

    UIToolbar.appearance().barTintColor = UIColor.darkGrayColor()
    UIToolbar.appearance().tintColor = UIColor.whiteColor()

    UITableView.appearance().backgroundColor = UIColor.blueColor()
    UITableView.appearance().tableFooterView = UIView(frame: CGRectZero)
    UITableViewHeaderFooterView.appearance().tintColor = UIColor.blueColor()

    return true
}

Answer 1

On the devices that have the button backgrounds, look in the Settings app under General > Accessibility. There is a Button Shapes switch. If that switch is ON, that's the cause of this behavior on those devices.

If that's the reason, there's really nothing you can do about it, and nothing you should want to do about it. It's up to the user if they want to make the interface look like this. It's a built-in option. Don't worry, be happy.