Don't want to bust balls, but or the love of god format your code better, both in the editor and when you post. You'll save everyone some sanity.

 var imagem0 : Texture; 
 var imagem1 : Texture; 
 var imagem2 : Texture; 
 var CurrentColor : boolean = true;
 
 function Update () {
     
     // switch colors
     
     if(Input.GetButtonDown("Fire2")) 
     { 
         if(renderer.material.mainTexture == imagem0) 
             renderer.material.mainTexture = imagem2; 
         else renderer.material.mainTexture = imagem1; 
         // ELSE RIGHT AFTER ANOTHER ELSE
         else renderer.material.mainTexture = imagem0; } } }

You have an else following an else, You probably meant to put an end curly brace after the first else.