How to check for two specific colliders and if its true changing the color on those three objects but not other instances with the same script attached?

I want to do a specific thing. I have random running letters falling down from the sky. Imagine something like Matrix. But when specific combinantion of numbers appears (909) I want them to turn red.

I have did following and it works partially.

On prefab with the mesh of number 0 I have attached following script

 public class RedNumberZero : MonoBehaviour
 {
     Renderer rend;
     public bool red;
     List <GameObject> currentCollisions = new List <GameObject> ();
     void Start()
      {
          rend = GetComponent<Renderer>();
      }
     
      void OnTriggerEnter (Collider col) {
  
          if (col.tag == "9")
          {
          // Add the GameObject collided with to the list.
          currentCollisions.Add (col.gameObject);
          }
 
          if (currentCollisions.Count == 2)
          {
              red = true;
              Color color = rend.material.color;
              rend.material.color = Color.red;
              Debug.Log("collision");
          }
  
          
      }

On prefab with number 9 mesh i have the following script

 public class RedNumberNine : MonoBehaviour
 {
     private bool zeroCol;
     Renderer rend;
     private RedNumberZero zeroScript;
     void Awake()
     {
         zeroScript = GameObject.FindObjectOfType<RedNumberZero> ();
     }
     // Start is called before the first frame update
     void Start()
     {
         rend = GetComponent<Renderer>();
     }
     void OnTriggerEnter (Collider col) {
         if (col.tag == "0")
          {
          zeroCol = true;
          Debug.Log("Coll 2");
          }
 
     }
 
     // Update is called once per frame
     void Update()
     {
         if(zeroScript.red == true && zeroCol == true)
         {
             ColorChange();
             
         }
     }
 
     void ColorChange()
     {
         Color color = rend.material.color;
         rend.material.color = Color.red;
     }
 }

It works strange. I cannot describe the behaviour thoroughly / because i dont really understand what exactly happening. But what the biggest problem actually is that if all of those conditionts are passed alll of my instances of prefabs on the scene with the script attached turn red. I want this to happen just and only on a place where combination "909" appears.

Any idea what i could do better?