Problem Changin Standard shader Alpha Channel

 _color.a = ((_time - 0)) * 1 / _size;
  
  this.transform.GetComponent<Renderer> ().material.SetColor("_Color", new Color (Random.Range (0f,1f), Random.Range (0f,1f), Random.Range (0f,1f), _color.a));

I'm trying to change the Unity 5 Standard Shader (Specular) Alpha channel, but it does nothing...

What this part of the code does is, change the alpha channel value with time, but the problem is that only the color changes, the alpha channel stays the same until i so much as click on the color, in the inspector, on the object material settings...

Is this a bug?? Please help me, i have been trying to fix this for at least 2 months with no results :C!