Collision problem

I made a game where the player goes through the platform when it changes color, but he did not return to normal when he leaves the platform, how can she return to normal when the player get through it? here my script:

using UnityEngine; using System.Collections;

public class Colortest : MonoBehaviour { public bool color = false;

// Use this for initialization void Start() { }

 // Update is called once per frame
 void Update()
 {
    if (color == true)
     {
         renderer.material.color = Color.blue;
     }
              
     }
 
 void OnCollisionEnter2D (Collision2D col)
 {
     if (col.gameObject.tag == "Player")
     {
         color = true;
     }
     }    

}