how to create color targeting script for a 2d sidescroll

I would like to create a script that targets a 2d sprite "enemy" and changes their color to red (slightly opaque red if possible) when you hit tab. When you hit tab again It will deselect the target turning the sprite image back to its original state (essentially no color) I have this code from a 3d tutorial hoping the transition would work. But it does not. I only get the script to cycle the enemy tags but never changes the color. I'm very new to coding, and any help would be FANTASTIC! HELP! hahah.

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 
 public class Targetting : MonoBehaviour {
     public List<Transform> targets;
     public Transform selectedTarget;
 
     private Transform myTransform;
 
     // Use this for initialization
     void Start () {
         targets = new List<Transform>();    
         selectedTarget = null;
         myTransform = transform; 
 
         AddAllEnemies();
     }
 
     public void AddAllEnemies()
     {
         GameObject[] go = GameObject.FindGameObjectsWithTag("Enemy");
 
         foreach(GameObject enemy in go)
             AddTarget(enemy.transform);
     }
 
     public void AddTarget(Transform enemy)
     {
         targets.Add(enemy);
     }
 
 
     private void SortTargetsByDistance()
     {
         targets.Sort(delegate(Transform t1,Transform t2) { 
                 return Vector3.Distance(t1.position, myTransform.position).CompareTo(Vector3.Distance(t2.position, myTransform.position)); 
                 });
     }
 
 
     private void TargetEnemy()
     {
         if(selectedTarget == null)
         {
             SortTargetsByDistance();
             selectedTarget = targets[0];
         }
         else 
         {
             int index = targets.IndexOf(selectedTarget);
 
             if(index < targets.Count -1)
             {
                 index++; 
             }
             else
             {
                 index = 0;
             }
             selectedTarget = targets[index];
         }
         
     }
 
     private void SelectTarget()
     {
         selectedTarget.GetComponent<SpriteRenderer>().color = Color.red;
     }
 
     private void DeselectTarget()
     {
         selectedTarget.GetComponent<SpriteRenderer>().color = Color.blue;
         selectedTarget = null;
     }
 
     // Update is called once per frame
     void Update()
     {
         if(Input.GetKeyDown(KeyCode.Tab))
         {
             TargetEnemy();
         }
     }
 
 }