dynamically changing texture of an object

I'm trying to make a GUI button that provides me change the texture of a GameObject... Any ideas?

I tried to use this code, but somehow when I click on button the sphere turns white, no texture...

 using UnityEngine;
 using System.Collections;
 
 namespace Vuforia
 {
     public class GUI_Button : MonoBehaviour 
     {
         GameObject Pokeball;
         Texture3D texture = (Texture3D) Resources.Load ("Resources/clouds1024");
 
         private void OnGUI() 
         {
             if (GUI.Button (new Rect (5, 15, 100, 25), "Pokebola")) {
                 Pokeball = GameObject.Find("Pokeball");
 
                 Pokeball.GetComponent<Renderer>().material.mainTexture = texture;
             
             }
         }
     }
 }