How do I make tiles that light up when gameobject touches them?

Hello! I'm making a 2D twinstick shooter, and i wanted a interesting background of tiles that light up and fades away when player and enemies move over them. I have two problems:

1: the change of colour and fade back seems only to happen the first time i runb over them with the gameobject i am using Mathf.SmoothStep to achieve the fading btw.

2: when i group the tiles together, it seems to have a big impact on performance. It laggs like hell when i drag the board of tiles around, and sometimes even unitu freezes up. The tiles are made up of a sprite render and a box collider that is a trigger.

Here is the code for the tiles:

 public class glow : MonoBehaviour {
     private SpriteRenderer s;
     public bool fading = false;
     private float startTime;
     private float t;
     float fadeTime = 4.0f;
     void Start () 
     {
         s = GetComponent<SpriteRenderer> ();
         startTime = Time.time;
         s.color = Color.black;
 
 
     }
         
     IEnumerator flash(float time)
     {
         yield return new WaitForSeconds (time);
 
     }
     void colourChange()
     {
         s.color = new Color (60.0f/255.0f, 200.0f/255.0f,200.0f/255.0f, 1.0f);
     }
 
     void colourFade()
     { 
         t = (Time.time - startTime) / fadeTime;
         s.color = new Color (Mathf.SmoothStep (60.0f/255.0f, 0f, t), Mathf.SmoothStep (200.0f/255.0f, 0f, t), Mathf.SmoothStep (200.0f/255.0f, 0f, t), 1.0f);
     
     }
 
     void OnTriggerEnter2D(Collider2D other)
     {
         if(other.gameObject.tag == "Player")
         {
             colourChange ();
 
         }
     }
     void OnTriggerExit2D(Collider2D other)
     {
         if(other.gameObject.tag == "Player")
         {
             fading = true;
             StartCoroutine(flash(4.0f));
         }
     }
         
 
 
     void Update () 
     {
         if(fading == true)
         {
             colourFade ();
         }
     }
 }
 

Thank you :)