change UIAlertcontroller background Color

Swift 5
Write just one line of code using UIAlertController extension.

alertController.setBackgroundColor(color: UIColor.black)

Full documentation: http://www.swiftdevcenter.com/change-font-text-color-and-background-color-of-uialertcontroller/

extension UIAlertController {

    //Set background color of UIAlertController
    func setBackgroundColor(color: UIColor) {
        if let bgView = self.view.subviews.first, let groupView = bgView.subviews.first, let contentView = groupView.subviews.first {
            contentView.backgroundColor = color
        }
    }

    //Set title font and title color
    func setTitlet(font: UIFont?, color: UIColor?) {
        guard let title = self.title else { return }
        let attributeString = NSMutableAttributedString(string: title)//1
        if let titleFont = font {
            attributeString.addAttributes([NSAttributedString.Key.font : titleFont],//2
                                          range: NSMakeRange(0, title.utf8.count))
        }

        if let titleColor = color {
            attributeString.addAttributes([NSAttributedString.Key.foregroundColor : titleColor],//3
                                          range: NSMakeRange(0, title.utf8.count))
        }
        self.setValue(attributeString, forKey: "attributedTitle")//4
    }

    //Set message font and message color
    func setMessage(font: UIFont?, color: UIColor?) {
        guard let message = self.message else { return }
        let attributeString = NSMutableAttributedString(string: message)
        if let messageFont = font {
            attributeString.addAttributes([NSAttributedString.Key.font : messageFont],
                                          range: NSMakeRange(0, message.utf8.count))
        }

        if let messageColorColor = color {
            attributeString.addAttributes([NSAttributedString.Key.foregroundColor : messageColorColor],
                                          range: NSMakeRange(0, message.utf8.count))
        }
        self.setValue(attributeString, forKey: "attributedMessage")
    }

    //Set tint color of UIAlertController
    func setTint(color: UIColor) {
        self.view.tintColor = color
    }
}

Swift 4.1 :

This is the best way works for me :

func testAlert(){
    let alert = UIAlertController(title: "Let's See ..",message: "It Works!", preferredStyle: .alert)
    let dismissAction = UIAlertAction(title: "Dismiss", style: .default, handler: nil)

    // Accessing alert view backgroundColor :
    alert.view.subviews.first?.subviews.first?.subviews.first?.backgroundColor = UIColor.green

    // Accessing buttons tintcolor :
    alert.view.tintColor = UIColor.white

    alert.addAction(dismissAction)
    present(alert, animated: true, completion:  nil)
}

For Objective C, the below code works like charm.

UIAlertController *alertController = [UIAlertController alertControllerWithTitle:@"Save changes?" message:nil preferredStyle:UIAlertControllerStyleAlert];

UIView *firstSubview = alertController.view.subviews.firstObject;

UIView *alertContentView = firstSubview.subviews.firstObject;

for (UIView *subSubView in alertContentView.subviews) { //This is main catch
    subSubView.backgroundColor = [UIColor blueColor]; //Here you change background
}

try this

Swift2 and below

let subview :UIView = alert.view.subviews. first! as UIView
let alertContentView = subview.subviews. first! as UIView
alertContentView.backgroundColor = UIColor.blackColor()

Objective -C

UIView *subView = alertController.view.subviews.firstObject; //firstObject
UIView *alertContentView = subView.subviews.firstObject; //firstObject
[alertContentView setBackgroundColor:[UIColor darkGrayColor]];

alertContentView.layer.cornerRadius = 5;

updated answer swift 3 and above

   let alert = UIAlertController(title: "validate",message: "Check the process", preferredStyle: .alert)
    let dismissAction = UIAlertAction(title: "Dismiss", style: .destructive, handler: nil)
    alert.addAction(dismissAction)
    self.present(alert, animated: true, completion:  nil)
    // change the background color
    let subview = (alert.view.subviews.first?.subviews.first?.subviews.first!)! as UIView
    subview.layer.cornerRadius = 1
    subview.backgroundColor = UIColor(red: (195/255.0), green: (68/255.0), blue: (122/255.0), alpha: 1.0)

output

iPhone

iPad