Changing images using a shader on a 2D canvas?

I'm trying to create a character select screen that uses a single square for each player and takes controller input to scroll through an array of images to select the character they want. I have most of it down. The trouble is that while the shader on the square reflects the image I want to see in the inspector, the image in the actual game doesn't change unless I toggle something in the shader inspector!

Here is my code, which includes the array for the actual fighter select.

 using System.Collections;
 using System.Collections.Generic;
 using System.Linq;
 using UnityEngine;
 using UnityEngine.UI;
 using UnityEngine.EventSystems;
 
 public class FighterSelection : MonoBehaviour {
 
     public int index = 0;
     public bool caninteract;
     public string Horiz;
     public string Vert;
     public string fighterfolder;
     public string P;
     public GameObject Im;
     public List<GameObject> fighterlist;
     public List<Texture> plist;
     public string TextureName;
 
     void Start (){ 
         
         caninteract = true;
         Texture[] pics = Resources.LoadAll<Texture> ("Images/Portraits");
         GameObject[] fighter = Resources.LoadAll<GameObject>(fighterfolder);
 
         foreach (GameObject f in fighter) {
             GameObject fightr = Instantiate(f) as GameObject;
             fightr.transform.SetParent(GameObject.Find(P).transform);
 
             fighterlist.Add (fightr);
             fightr.SetActive (false);
             fighterlist [index].SetActive (true);
 
             foreach (Texture i in pics) {
                 Texture pc = Instantiate (i) as Texture;
                 plist.Add (pc);
 
             }
         }
     }
     void Update(){
 
         if (caninteract == true);
         {
             if (Input.GetAxis (Horiz) > 0f) {
                 ToggleRight ();
                 StartCoroutine (select ());
                 }
             if (Input.GetAxis (Horiz) < 0f) {
                 ToggleLeft ();
                 StartCoroutine (select ());
             } 
         } 
 
         Texture portrait = (Texture)plist [index];
         Im.GetComponent<Image> ().material.mainTexture = portrait;
         Im.GetComponent<Image> ().material.SetColor ("_Color", Color.clear);
     }
         IEnumerator select ()
     {
         yield return new WaitForSeconds (0.75f);
         caninteract = true;
     }
 
     public void ToggleLeft()
     {
         fighterlist [index].SetActive (false);
         index --;
         caninteract = false;
         if (index < 0) {
             index = fighterlist.Count - 1;
         }
             fighterlist [index].SetActive (true);
     } 
     public void ToggleRight ()
     {
         fighterlist[index].SetActive (false);
         index++;
         caninteract = false;
         if (index == fighterlist.Count) {
             index = 0;
         }
             fighterlist [index].SetActive (true);
     } 
 }

The variables I put in the inspector are to separate the script by player. I also have a problem getting the waitforseconds thing to work, but that can wait. What am I doing wrong?