Take a look at displayObject.blendMode property: http://livedocs.adobe.com/flex/3/langref/flash/display/BlendMode.html#INVERT
Use a custom cursor with that property set to BlendMode.INVERT
Update:
here is the solution
Cursor class:
package test
{
import flash.display.BlendMode;
import flash.display.Graphics;
import flash.display.Sprite;
public class InvertCursor extends Sprite
{
public function InvertCursor()
{
super();
draw();
blendMode = BlendMode.INVERT;
}
public function draw():void {
var g:Graphics = graphics;
g.clear();
g.beginFill(0);
g.lineStyle(0);
g.drawCircle(0, 0, 10);
g.endFill();
}
}
}
Usage:
import mx.managers.CursorManager;
import test.InvertCursor;
private function setInvertCursor():void {
CursorManager.setCursor(InvertCursor);
}