Changing Second Material

Hi! I have a object with 2 materials on it, and I want to change the second material via code. This is the code I'm using:

 public class ChangeColorGreen : MonoBehaviour {
     public PlayerScript playerScript;
     public Material[] materials;
     public Renderer rend;
 
     void Start () {
     
     }
 
     void Update () {
         if (playerScript.isGreen == true) {
             rend.sharedMaterials[1] = materials[0];
         }
     }
 }

When I attempt to change the second material, absolutely nothing happens:

But when I change the code to

 rend.materials[1] = materials[0];

This happens:

But I can change the first element perfectly fine: http://i.imgur.com/n5kHuLf.png?1 (changed to imgur becuase the site stopped me from uploading pictures)

So does anyone have an insight on this? Thanks!