haxe cannot click transparent sprite only in flash

PlayState.hx

package;

import flixel.FlxG;
import flixel.FlxSprite;
import flixel.FlxState;
import flixel.util.FlxColor;

class PlayState extends FlxState
{
	var square: FlxSprite;
	
	var iter = FlxColor.colorLookup.iterator();
	
	override public function create():Void
	{
		square = new FlxSprite(0, 0);
		square.makeGraphic(40, 40, FlxColor.TRANSPARENT);
		add(square);
		super.create();
	}

	override public function update(elapsed:Float):Void
	{
		super.update(elapsed);
		
		if (FlxG.mouse.justPressed && FlxG.mouse.overlaps(square)) {
			square.makeGraphic(40, 40, FlxColor.WHITE);
		}
		
	}
}