OnMouseEnter and OnMouseExit for multiple materials

Hey guys! I am writing a script to highlight the object in the scene. The object has 3 materials. So, using the example from the documentation for OnMouseOver ( https://docs.unity3d.com/ScriptReference/MonoBehaviour.OnMouseOver.html ) I wrote the script, which has the following idea:

MeshRenderer gets all materials from the object and puts in a list. Then in the for-loop the color of each material is added to the list of the initial materials' colors. In OnMouseEnter method each initial material is assigned a new color. And in the OnMouseExit (i haven't completed it yet) the initial materials are to be assigned to the object. Here is the script:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using System.Linq;
 
 public class Selection : MonoBehaviour
 {
 
     public List<Material> bldg_mats_init;
     public List<Color> mat_color_init;
     private Material mat;
     Color colorSelection = Color.red;
     MeshRenderer m_Renderer;
     
     void Start()
     {
         m_Renderer = GetComponent<MeshRenderer>();
         List<Material> bldg_mats_init = m_Renderer.materials.ToList();
         
         Debug.Log("Numer of bldg_mats_init:" + bldg_mats_init.Count);
 
         for (int i = 0; i < bldg_mats_init.Count; i++)
         {
             mat = bldg_mats_init[i];
             mat_color_init.Add(mat.color);
 
             Debug.Log("Stored colors:" + mat_color_init.Count);        
         }
         Debug.Log("Number of init mat colors:" + mat_color_init.Count);
     }
     
      private void OnMouseEnter()
     {
         Debug.Log("Number of init materials (OME):" + bldg_mats_init.Count);
 
         Debug.Log("Number of init colors (OME):" + mat_color_init);
 
         for (int i=0; i < bldg_mats_init.Count; i++)
         {
             material_bldg = bldg_mats_init[i];
             m_Renderer.material.color = colorSelection;
         }
     }
     private void OnMouseExit()
     {
         for (int i = 0; i < bldg_mats_init.Count; i++)
         {
 
         }
 
     }
 }

And it doesn't work. So the Debug.Log in the OnMouseOver method doesn't return the right number of materials obtained in Start. What could be the problem?

Thank you in advance!