how to change material on an object in unity 5

SO I am making this simple game and instead of making a padlock I thought I could have the objects on my world map scene I want the object color to be different to show that it is "locked." Bellow is the script that is on the objects that will change color.

using UnityEngine;

using System.Collections;

using UnityEngine.SceneManagement;

public class LevelLoader : MonoBehaviour {

 public int LeveltoLoad;
 public Material lockedlevel;
 private string loadPrompt;
 private bool inRange;
 private int completedLevel;
 private bool canLoadLevel;
 void Start()
 {
     completedLevel = PlayerPrefs.GetInt ("Level Completed");
     canLoadLevel = LeveltoLoad <= completedLevel ? true : false;
     if (!canLoadLevel) 
     {
         Instantiate (lockedlevel); 
         {
             gameObject.GetComponent<Renderer> (lockedlevel).material;
         }
     }
 }
 void OnTriggerStay(Collider other)
 {
     inRange = true;
     if (canLoadLevel) {
         loadPrompt = " (Space) to load level " + LeveltoLoad.ToString ();
     }
     else
     {
         loadPrompt = "level_" + LeveltoLoad.ToString () + "is locked";
     }
 }
 void Update()
 {
     if (Input.GetButtonDown ("Action") && inRange)
     {
         SceneManager.LoadScene ("level_" + LeveltoLoad.ToString());
     }

}

 void OnTriggerExit()
 {
     inRange = false;
     loadPrompt = "";
 }

 void OnGUI()
 {
     GUI.Label (new Rect(30, Screen.height * .9f, 200, 40),loadPrompt);
 }

}

Any help to figure out what I am missing would be great! Thanks.