Changing material at runtime messes up with prefab materials [Solved]

Hi guys, I have a problem. I am making a Bubble Breaker game and so far I have made only the basic bubbles (red, green, blue, yellow, magenta). I have separate materials and prefabs for each bubble. Now I am trying to create a ChameleonBubble which changes it's color to one of the basic ones each turn.

Here is the code for adding the ChameleonBubble in the game scene:

 public void AddChameleonBubbleAtRandomPosition()
     {
         int row = UnityEngine.Random.Range(0, Rows);
         int column = UnityEngine.Random.Range(0, Columns);
         Destroy(this.bubbles[row, column].GameObject);
         this.bubbles[row, column] = null;
 
         GameObject randomNormalBubble = this.GetRandomNormalBubblePrefab();
 
         GameObject chameleonBubblePrefab = this.GetBubblePrefab(GameObjectName.ChameleonBubble);
         
         GameObject newChameleonBubbleGameObject =
             (GameObject) Instantiate(chameleonBubblePrefab, Vector3.zero, Quaternion.identity);

         // Here I change the color of the chameleon bubble
         // to a random one from the normalBubblePrefabs
         newChameleonBubbleGameObject.renderer.material = randomNormalBubble.renderer.material;
         newChameleonBubbleGameObject.transform.parent = this.transform;
         newChameleonBubbleGameObject.transform.localPosition = new Vector3(column, -row, 0);
 
         this.bubbles[row, column] =
             new ChameleonBubble(row, column, this.GetTypeOfBubble(randomNormalBubble), newChameleonBubbleGameObject);
     }

Everything works fine when I run the scene. The problem is that when I stop the scene, the materials of the prefabs of the normal bubbles are reset (In the MeshRenderer Component there is a message "Missing Material". That is only for the prefabs which materials have been used to create the new ChameleonBubble. For example (if in the scene a yellow ChameleonBubble appears, then only the material of the yellow normal bubble prefab is missing, the other normal bubble prefabs are ok). Do you know what the problem might be? I even tried "newChameleonBubbleGameObject.renderer.material = new Material(randomNormalBubble.renderer.material)" but that didn't work either.