GetComponent is missing custom function Call. Why?

OK strange issue this time. I am practicing with getcomponent and findwithtag (or find) commands, in order to apply a custom function created in the script of a first object (in this case a cube) to the second (a capsule object). Unfortunately this is not working and I don't know why, so I can't call my custom function from a script to another.

In my scene I have a capsule and a cube placed in its public gameobject slot and tagged "cubo"(the cube) and "capsula" (the capsule).

The custom function I created is called ChangeColorObj, it add a color to a GameObject selecting it randomly from a color array. Here u are the script of the cube object:

 using UnityEngine;
 using System.Collections;
 
 public class randomcolor : MonoBehaviour {
     public GameObject m_Cube = null;
     public int m_RandomEngine = 0;
     public Color[] m_ColorTank;
     public Color m_ColorStart;
         
     
     
     void Start () {
     
         ChangeColorObj (m_RandomEngine, m_Cube, m_ColorStart, m_ColorTank);
 
         
     }
     
     
     
         public void ChangeColorObj (int arandom, GameObject cb, Color prefab, Color [] list ) 
     {
         arandom = Random.Range (0, list.Length);
         prefab = list[arandom];
         cb.renderer.material.color = prefab;
     }
     
     
     void Update () {
     
     }
 }

and now the script of the capsule object:

 using UnityEngine;
 using System.Collections;
 
 public class capsularandom : MonoBehaviour {
     
     public GameObject m_Capsule = null;
     public int m_Capsualx = 0;
     public Color[] m_ColorTankX;
     public Color m_StartColorX;
     
     
     void Start () {
     
         
     //m_Capsula.GetComponent<randomcolor>().CambiaColorePerOBJ(m_Capsualx, m_Capsula, m_Inizialx, m_SerbatoioColorx);
     GameObject.Find("Capsule").GetComponent<randomcolor>().ChangeColorObj(m_Capsualx,GameObject.Find("Capsule"), m_StartColorX, m_ColorTankX);
     //GameObject.FindWithTag("capsula").SendMessage("CambiaColorePerOBJ",(m_Capsualx, GameObject.FindWithTag("capsula"), m_Inizialx, m_SerbatoioColorx));
     
     }
     
 
     void Update () {
     
     }
 }

notice that there are 2 commented strings: they are other attempts that doesn't works too. The scripts are without errors, because if I press f8, all seems to be ok. But only the cube change its color, instead the capsule still remains gray. :(

Anyone knows why?

Thanks for the attention

regards

Matthew