Alpha not displaying when changed in code, unless changed manually in the inspector

Hello there !

I've come across many problems with alpha in unity, and with a lot of reading I've manage to get rid of most of it.. but one is still there :

I've made this script :

 public class Alpha : MonoBehaviour {
 
     public Renderer r;
 
     void Start() 
     {
         if(r == null) r = GetComponent<Renderer>();
         r.material.SetFloat("_Mode", 2.0f);
     }
 
     IEnumerator FadeOut()
     {
         float a = 1;
         while(a > 0)
         {
             a -= 0.01f; 
             Color c = r.material.color;
             c.a = a;
             r.material.color = c;
             yield return new WaitForEndOfFrame();
         }
         StartCoroutine("FadeIn");
     }
 
     IEnumerator FadeIn()
     {
         float a = 0;
         while(a < 1)
         {
             a += 0.01f; 
             Color c = r.material.color;
             c.a = a;
             r.material.SetColor("_Color", c);
             yield return new WaitForEndOfFrame();
         }
         StartCoroutine("FadeOut");
     }
 }

Then, I instantiate an object and put this script on it, and call StartCoroutine :

 go = GameObject.Instantiate(go, p.Location, Quaternion.Euler(p.Rotation)) as GameObject;
 go.name = (p.isMobile ? "mob_" : "item_") + p.Serial.ToString();
 
 Renderer[] rs = go.GetComponentsInChildren<Renderer>();
 for(int i = 0; i < rs.Length; i++)
 {
     Alpha a = rs[i].gameObject.AddComponent<Alpha>();
     a.r = rs[i];
     a.StartCoroutine("FadeIn");
 }

And this doesn't work ! The value alpha value changes in the inspector, but nothing change in the scene. Then if I manually change the alpha in the inspector, the display works and the object starts fading in and out as it should...

Any idea?