ActionScript 3.0 :: Making A Button That Will Light Up When Scroll Over It

So I was working on making a button that will light up when I scroll over it, not instantly but more realisticly. The button starts out gray and when I scroll over it I want it to fade to red.

So I made a new AS3 Flash file and drew a simple gray box, made it a button, and inside the button I made the box a Movie Clip, shape tweened it so that it fades from gray to red in a period of 5 frames.

Now I'm just stuck on the scripting part, I made a new layer inside the movie clip for the script and have this typed in:

Code:
import flash.events.MouseEvent;
rectangle_mc.addEventListener(MouseEvent.MOUSE_OVER, mcOver);
function mcOver(event:MouseEvent)void{
play.rectangle_mc
}

I don't even know what import flash.events.MouseEvent; even means.

But what I'm trying to accomplish here is to make the shape tween Movie Clip only play when the cursor is over the button. So that when I scroll over the button it fades from gray to red. Sounds like a plan, but I can't figure out the function part where it says play.rectangle_mc,