Changing Color/Material using HDRP,Modify The Color of a HDRP material

I am currently trying to modify the color of a material on my objects. I tried by changing directly the color.. No result Changing the material with a new material that has the right color, No results either.

I tryied to google Documentation for referencing of the HDRP properties and I found nothing either.

So here's my code :

 /// <summary>
     /// Set the color for the gameObjects in the path
     /// </summary>
     /// <param name="gridsToColor"> An array containing the grid of prefabs to color</param>
     public void SetGridColor(List<GameObject> gridsToColor)
     {
         for(int i = 0; i < gridsToColor.Count; i++)
         {
             gridsToColor[i].GetComponent<Renderer>().materials[0] = pathColorOuterLayer;
             gridsToColor[i].GetComponent<Renderer>().materials[1] = pathColorInnerLayer;
 
         }
     }

I simply try to assign a new material to the gameobject. With some debug it finds the right gameObject but simply the material is never assigned.... And I do NOT want transfer my project to a downgrade version