Invoke Random function

actually my code is this

void OnTriggerStay (Collider other){

             if (Input.GetButtonDown ("giallo")) { 
                 murobase.SetActive (false);
                 muro_blu.SetActive (false);
                 muro_arancione.SetActive (false);
                 muro_giallo.SetActive (true);
             } else {
                 if (Input.GetButtonDown ("arancio")) {
                     murobase.SetActive (false);
                     muro_blu.SetActive (false);
                     muro_arancione.SetActive (true);
                     muro_giallo.SetActive (false);
                 } else {
                     if (Input.GetButtonDown ("blu")) {
                         murobase.SetActive (false);
                         muro_blu.SetActive (true);
                         muro_arancione.SetActive (false);
                         muro_giallo.SetActive (false);
                     }
                 }
     }

     }

but i'd like to change the gameobjects with a only button, so I tried to do

void gialloON (){
murobase.SetActive (false);
muro_blu.SetActive (false);
muro_arancione.SetActive (false);
muro_giallo.SetActive (true);

 }

 void arancioneON(){
     murobase.SetActive (false);
     muro_blu.SetActive (false);
     muro_arancione.SetActive (true);
     muro_giallo.SetActive (false);
 }
 void bluON (){
     murobase.SetActive (false);
     muro_blu.SetActive (true);
     muro_arancione.SetActive (false);
     muro_giallo.SetActive (false);
 
 }
     void OnTriggerStay (Collider other)  {                          
                 if (Input.GetButtonDown ("button")){

Invoke.... //i have to say,if you press button one time invoke void bluON, if you press another time invoke void arancioON, the tird time voidgialloON, and so on random, how can I do it?

}