ActionScript 3.0 :: Flash Autofill Polygon In Real Time

I am creating a game where I have some red balls on the screen and some blue balls on the screen and I would like to draw a polygon around all balls of the same color and have this polygon automatically fill as soon as the polygon shape is closed. How to achieve this as I haven't really done much with the drawing API before. My current code will allow me to draw a polygon and for it to fill when I release the mouse but what I would like it to do is automatically fill as soon as the shape is closed.

Here is my code so far
Code:
var graphix = new MovieClip();
addChild(graphix);
var points:Array = [];
stage.addEventListener(MouseEvent.MOUSE_DOWN, startDrawing);
[Code] .....