UIText Color Alpha not working

I want to make instantiate and fade out a UIText in unity but its not working

 GameObject score=Instantiate(Score,posScore,Quaternion.identity) as GameObject;
 
  StartCoroutine(FadeOut(score));
 
   IEnumerator FadeOut(GameObject score)
     {
   Color alpha = score.GetComponent<Text>().color;
         while (alpha.a > 0)
         {
           alpha.a = 0;
           alpha.a -= Time.deltaTime / time;
            yield return null;
        }
     }

I instantiate a Score object which is a Text Prefeb and then try to disapear slowly but my code is not working.