title: Customise the color of buttons in the RPPreviewViewController (ReplayKit)
body: <p>I have recorded a video sequence with RPScreenRecorder. Everything works perfectly fine.</p>
  <p><strong>Now I want to customize the UI of the preview controller.
  How can I change the color of the cancel and save buttons?
  Yeah, in general I know how to change the color of a UIBarButtonItem:</strong></p>
  <pre><code>let cancelBtn = UIBarButtonItem(barButtonSystemItem: .cancel, target: self, action: #selector(self.dismissView))
  cancelBtn.setTitleTextAttributes([NSAttributedString.Key.foregroundColor: UIColor.red], for: .normal)
  </code></pre>
  <p><strong>But I can not find the references of the buttons in the preview (RPPreviewViewController).</strong></p>
  <pre><code>func stopRecorder() {
          recorder.stopRecording { [unowned self] (preview, error) in            
              guard let previewVC = preview else {
                  return
              }
              previewVC.previewControllerDelegate = self
              previewVC.modalPresentationStyle = .fullScreen
              self.present(previewVC, animated: true, completion: nil)
          }
      }
  ``
  </code></pre>