Why is the color component not working?

Hey Unity community,

I'm having trouble with adding color to my objects in my script

Here's the script (appreciate the help):

using System.Collections; using System.Collections.Generic;

public class Targetting : MonoBehaviour { public List 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 SortTargetByDistance()
 {
     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) {

         SortTargetByDistance ();
         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<Renderer>().material.color = Color.red;
 }


 // Update is called once per frame
 void Update () {
 
     if(Input.GetKeyDown (KeyCode.Tab)) {
         TargetEnemy ();
     }
 }

}

Thanks for the help!