Using a Color Picker

I have been playing around with Interface Builder, and I have begun to understand how things work, instead of thinking that magic pixies were behind it. There is still one problem that bothers me, though.

The ADC-provided sample code DragItemAround also has functionality to change the color of the rectangle. I see the method that does this, but I can not see where or how this method gets called by the color picker!

Thanks in advance!

Hi! You see method changeColor:, but how to call it from app?
Call menu item Action->Show Colors and change color with opened color panel.