make the object know its selected (C#)

So i have a targeting script. What code should i use to inform that an object is selected ? this is what i have so far..

 using UnityEngine;

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

public class targeting : 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 SortTargetsByDistance() {
     targets.Sort(delegate(Transform t1, Transform t2) {
             return Vector3.Distance(t1.position, myTransform.position).CompareTo(Vector3.Distance(t2.position, myTransform.position));
             });
 }
 
 
 
 
 //if we do not have an enemy targeted ywt, then find the clostest one and target him
 //if we do have an enemy targeted, then get the next target
 //if we have the last target in the list, then get then first target in the list
 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;
         }
         DeselectTarget();
         selectedTarget = targets[index];
     }
     SelectTarget();
 }
 
 private void SelectTarget() {
     selectedTarget.renderer.material.color = Color.red;
 
     
 }
 
 private void DeselectTarget() {
     selectedTarget.renderer.material.color = Color.white;
     selectedTarget = null;
 }
 
 // Update is called once per frame
 void Update () {
     if(Input.GetKeyDown(KeyCode.Tab)) {
         TargetEnemy();
     }
 }

}

Its from BirgZerg..

how do i make it so when it selects an object, that object knows that its selected.

i want to create a quest system in which you need to select the people and then left click to make the dialogue apear for each object that can speek. Please Help!