title: Change Background Color of the UIAlertController
body: <p>my code is </p>
  
  <pre><code>    UIAlertController *alert = [UIAlertController
                                   alertControllerWithTitle:@"Touch ID for Eceipt" message:@"Touch ID or Enter Password" preferredStyle:UIAlertControllerStyleAlert];
  
      UIAlertAction *cancelButton = [UIAlertAction
                                  actionWithTitle:@"Cancel"
                                  style:UIAlertActionStyleDefault
                                  handler:^(UIAlertAction * action) {
                                      //Handle your yes please button action here
                                  }];
      alert.view.tintColor=[UIColor blueColor];          
      alert.view.backgroundColor=[UIColor whiteColor];   //this code changes the alert view color
      alert.view.layer.cornerRadius=10;
      [alert addAction:cancelButton];
      [self presentViewController:alert animated:YES completion:nil];
  </code></pre>
  
  <p>by this code, I can achieve a "blue coloured Cancel Button" and a white coloured alert view and a gray coloured background..</p>
  
  <p>What i need is more dark Colour BG.
  here is my output screenshot <a href="https://i.stack.imgur.com/A2lB5.png" rel="nofollow noreferrer">above_code_output_screenshot</a>
  i Need the BG like this screenshot <a href="https://i.stack.imgur.com/moQko.png" rel="nofollow noreferrer">actually_what_i_need_is_this_output</a></p>