Turn-based-RPG-styled movement area color change

As the question implies, I'm trying to make Unity (2020.1.6f1) recreate something like this: This is what I've achieved so far: The catch is, I've not been able to make every plane's mesh collider inside the player's movement area turn blue at the same time; they only do so when the mouse passes over them. The code right now:

 using UnityEngine;
 
 public class GrassBehaviour : MonoBehaviour
 {
     public GameObject player;
     public Vector3 playerOriginalPosition;
     public Vector3 playerMaxPosition;
     public Vector3 grassSelectedPosition;
     public MeshRenderer[] rendArray;
     public bool comparePos;
     public bool mouseOver;
     public bool mouseExit;
     public Vector3 comparePos_2;
     public Vector3 comparePos_3;
     public void Start()
     {
         player = GameObject.FindGameObjectWithTag("Player");
     }
     public void FixedUpdate()
     {
         playerOriginalPosition = player.transform.position;
         playerMaxPosition = new Vector3(playerOriginalPosition.x + 2f, 0.5f, playerOriginalPosition.z + 2f);
         grassSelectedPosition = new Vector3(gameObject.transform.position.x, 0.5f, gameObject.transform.position.z);
         rendArray = gameObject.GetComponents<MeshRenderer>();
         comparePos = Vector3.Distance(playerMaxPosition, playerMaxPosition - (grassSelectedPosition - playerOriginalPosition)) < Vector3.Distance(playerMaxPosition, playerOriginalPosition);
         comparePos_2 = new Vector3((playerMaxPosition - playerOriginalPosition).x, 0.5f, (playerMaxPosition - playerOriginalPosition).z);
         comparePos_3 = new Vector3((float)(playerMaxPosition.x - playerMaxPosition.x - (grassSelectedPosition.x - playerOriginalPosition.x)), 0.5f, (playerMaxPosition.z - playerMaxPosition.z - (grassSelectedPosition.z - playerOriginalPosition.z)));
         if (comparePos==true)
         {
             rendArray[rendArray.Length * (int)playerMaxPosition.magnitude].material.color = Color.red;
             
         }       
     }
     public void OnMouseOver()
     {   
         if (comparePos == true)
         {
             mouseOver = true;
             gameObject.GetComponent<MeshRenderer>().material.color = Color.blue;
         }
         else
         {
             mouseOver = false;
             return;
         }
     }
     public void OnMouseExit()
     {
         if(comparePos == false)
         {
             mouseExit = true;
             gameObject.GetComponent<MeshRenderer>().material.color = Color.green;
         }
         else
         {
             mouseExit = false;
             return;
         }
     }
     public void OnMouseDown()
     {
         if (comparePos == true)
         {
             player.transform.position = new Vector3(gameObject.transform.position.x, player.transform.position.y, gameObject.transform.position.z);
         }
         else
         {
             return;
         }
     }
 }

As you'll no doubt notice, I'm not much into vectors yet -.- I humbly await an answer (or a correction, I'm afraid).