How do I change the alpha channel of a color in a color picker dialog?

I've made a Color Picker in C#, but s开发者_如何学Goomeone asked me to make an Alpha property. So far it works great, except for the part of the Alpha property itself.

The question is: How do I change the ColorDialog.Color.A by scrolling up and down a ScrollBar?

Use the ValueChanged event on the ScrollBar class.