When you create a macOS project that uses storyboards, each window is called a view, which has a border. Two ways to modify the border of a view is to change its width and change its color.
To change the view’s border width, you need to use the borderWidth property like this:
One way to make it easy to change the width of a border is to use a slider. Then create an IBOutlet for that slider along with an IBAction method like this:
To change the view’s border color, you need to use the borderColor property like this:
The simplest way to change the border color is through a color well. Just create an IBOutlet and an IBAction method for that color well, in addition to overriding the changeColor function like this:
If you have a slider and a color well on your view, users can drag the slider back and forth to modify the border width and click on the color well to choose a different color for that border. You can download a sample program that shows how this works:
BorderSetting sample program.