enable Blur effect when Esc button pressed (Windows Phone 8)

Hi, i have a FPS char that contains a Blur effect on the Main Camera which i want to active the Blur effect when i press the back button so i don't how to do it and here's my super simple code :

 using UnityEngine;
 using System.Collections;
 
 public class QuitOnGui1 : MonoBehaviour {
 
     public GameObject Yes;
     //public Blur blur;
 
     void Update () {
         if (Input.GetKeyDown (KeyCode.Escape))
             //blur = GetComponent<Blur>();
             //blur.enabled = true;
             //GetComponent<Blur>().enabled = true;
             Yes.SetActive (true);
          
         }
     }