@IBAction func changeBackgroundColorOnTap(_ sender: Any) {

        var aquaColor = blueView.backgroundColor

        if isBlue == true {

            blueView.backgroundColor = greenView.backgroundColor

        } else {

            blueView.backgroundColor = UIColor(red: 0/255.0, green: 128/255.0, blue: 255/255.0, alpha: 1)

        }
        isBlue = !isBlue
    }

    @IBAction func didBeginPanGesture(_ sender: UIPanGestureRecognizer) {

        let point = sender.location(in: view)

        greenView.center = CGPoint(x: point.x, y: point.y)

    }