Invert The Color Of A GUIText Crosshair?

So, my problem is my GUIText "crosshair" (Placeholder for a real one) isn't very visible under normal circumstances, no matter what I change the color to. So I thought I would have the color of my crosshair to be the inverted color of what I look at, so as to be able to see the crosshair easily, like in the game Minecraft. If you don't get what I mean, here is the desired result:

I've tried this code, but it seems to always become black:

 var Crosshair : GUIText;
 
 function Start () {
 
 }
 
 function Update () {
 
     var hit : RaycastHit;
     var ray : Ray = Camera.main.ScreenPointToRay(Vector3(Screen.width*0.5, Screen.height*0.5, 0));
     var dir : Vector3 = ray.direction;
 
     if (Physics.Raycast (transform.position, dir, hit, 100))
     {
         Crosshair.color = hit.gameObject.renderer.material.color;
     }else{
         Crosshair.color = Color.black;
     }
 
 }
 
 function InvertColor (color : Color) : Color {
     return Color (1.0-color.r, 1.0-color.g, 1.0-color.b);
 }