Object modified in script not modified in scene

Hello guys, I have a problem, and I don't know how to solve it.

I have a very basic code : using UnityEngine; using System.Collections;

 public class LightBallScript : ObjectScript {
 
     bool isRed = false;
     Renderer rend;
 
     void Start () {
         rend = GetComponent <Renderer> ();
         rend.material.EnableKeyword ("_Emission");
     }
 
     public override void ActivateObject () {
         if (isRed) {
             Debug.Log ("red --> black");
             rend.material.SetColor ("_Emission", Color.black);
             rend.material.SetFloat ("_Emission", 0);
             isRed = false;
         } else {
             Debug.Log ("black --> red");
             rend.material.SetFloat ("_Emission", 1);
             rend.material.SetColor ("_Emission", Color.red);
             Debug.Log (rend.material.GetColor ("_Emission"));
             isRed = true;
         }
         transform.position.Set (transform.position - Vector3.up);
     }
 }

My player calls the method ActivateObject. I checked that it was called with a debug.log . With debug.log, I checked that the gameobject was a "LightBall" (basically a sphere) and that the material was the "LightBall Material". I also checked that the emission color was changed to red.

But, in the scene, none of these modifications occured : the lightball didn't move, nor change its color.

I never got any problem like that, so I don't know where to search.

Thanks for your answers !