Ok so I have this alert that I am using and I want the background of it to be black not grey like it is. I have managed to change the colour of the text for the title and the me
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)
}