Click object to change colour.

Hi, I was just wondering does anyone know what code I would need to add to change the colour of myRedCircle when myBlueSquare is clicked?

The code I have already is below.

import flash.events.MouseEvent;
var myBlueSquare = new BlueSquare();
var myRedCircle = new RedCircle();
myBlueSquare.x= 50;
myBlueSquare.y=350;
myRedCircle.x=300;
myRedCircle.y=350;
myBlueSquare.addEventListener(MouseEvent.MOUSE_DOWN, doClick);
function doClick(e:MouseEvent):void
{
  
}