How do I get the screen to fade in when a trigger is triggered?

When the player walks into the trigger TeleportToL2, I need the screen to turn black and then fade in. The script on the trigger so far:

 #pragma strict
 
 var TeleportToL2Dest: Transform; // drag the destination empty here
   
 function OnTriggerEnter(other : Collider) 
     {
         if (other.tag == "Player") 
         {   
             // move and align the player to the destination empty GO
             other.transform.position = TeleportToL2Dest.position;
             other.transform.rotation = TeleportToL2Dest.rotation;
         }        
     }

I found a script off of Google, but it only fades as soon as the scene starts:

 #pragma strict
  
  // FadeInOut
  
  var fadeTexture : Texture2D;
  var fadeSpeed = 0.2;
  var drawDepth = -1000;
  
  private var alpha = 1.0; 
  private var fadeDir = -1;
  
  function OnGUI(){
      
      alpha += fadeDir * fadeSpeed * Time.deltaTime;  
      alpha = Mathf.Clamp01(alpha);   
      
      GUI.color.a = alpha;
      
      GUI.depth = drawDepth;
      
      GUI.DrawTexture(Rect(0, 0, Screen.width, Screen.height), fadeTexture);
  }

What would the code be to apply this script to only work when the TeleportToL2 trigger is triggered?