I don't think there are many people who develop real-world projects using AS3 alone. Flash is not Java. It's not a general purpose programming platform. ActionScript exists to supplement Flash's core abilities. If you're trying to do things in a "pure-AS" matter you're probably going up the wrong street.

Typically, one would create the visuals of an app in Flash Professional. Then behaviors are attached to the objects on the stage via ActionScript.

Here's what an applet might look like:

Actionscript Code:
package
{
    import fl.controls.ColorPicker;
    import fl.events.ColorPickerEvent;
    
    import flash.display.SimpleButton;
    import flash.display.Sprite;
    import flash.events.MouseEvent;
    import flash.net.FileReference;
    
    public class Editor extends Sprite
    {
        public var saveButton:SimpleButton;
        public var openButton:SimpleButton;
        public var colorPicker:ColorPicker;     
        public var photo:Sprite;
        
        public function Editor() {
            saveButton.addEventListener(MouseEvent.CLICK, onSaveButtonClick, false, 0, true);
            openButton.addEventListener(MouseEvent.CLICK, onOpenButtonClick, false, 0, true);
            colorPicker.addEventListener(ColorPickerEvent.CHANGE, onColorPickerChange, false, 0, true);
        }
        
        protected function onSaveButtonClick(e:MouseEvent):void {
            var fileRef:FileReference = new FileReference;
            fileRef.save('Hello world', 'something.txt');
        }
        
        protected function onOpenButtonClick(e:MouseEvent):void {
            var fileRef:FileReference = new FileReference;
            fileRef.browse();
        }
        
        protected function onColorPickerChange(e:ColorPickerEvent):void {
            photo.opaqueBackground = e.color;
        }
    }
}

This app doesn't do much. It just opens up a file selection selection dialog box when the Save or Open button is clicked. I also tossed in a color picker since that's what you're looking for. All it does is change the background color of a photo.

Looking at the code, you might wonder: where are the UI components coming from? They're declared in the class, but never created. The answer: Flash Professional will create them for you. Here're the source files:

https://dl.dropbox.com/u/80776822/Editor.zip

If you haven't installed Flash Professional, it's probably time to do so. Should check out some tutorials as well, especial on how to use the FP + FB combo.