Highlighting prefabs with different colors when a first person player looks at them,Highlighting objects programatically with different materials when the first person player looks at them

I want to highlight the objects with the selectable tag when the player looks at them. There are two types, they are either red or blue. I want to highlight them with a lighter shade of their default material. I have the following code, but it doesn't work:

 public class SelectionManager : MonoBehaviour
 {
     [SerializeField] Material highlightedRed;
     [SerializeField] Material highlightedBlue;
     [SerializeField] string selectableTag = "Selectable";
     [SerializeField] Material defaultRed;
     [SerializeField] Material defaultBlue;
     [SerializeField] GameObject redBocce;
     [SerializeField] GameObject blueBocce;
 
     private Transform _selection;
 
     void Start()
     {
         var blueRenderer = blueBocce.GetComponent<MeshRenderer>();
         var redRenderer = redBocce.GetComponent<MeshRenderer>();
 
         redRenderer.material = defaultRed;
         blueRenderer.material = defaultBlue;
         Update();
     }
     void Update()
     {
         if(_selection != null){
             var selectionRenderer = _selection.GetComponent<MeshRenderer>();
             if(selectionRenderer.material == highlightedBlue){
                 selectionRenderer.material = defaultBlue;
             }
             else if(selectionRenderer.material == highlightedRed){
                 selectionRenderer.material = defaultRed;
             }
             _selection = null;
         }
         var ray = Camera.main.ScreenPointToRay(Input.mousePosition);
         RaycastHit hit;
         if(Physics.Raycast(ray, out hit)){
             var selection = hit.transform;
             if(selection.CompareTag(selectableTag)){
                 var selectionRenderer = selection.GetComponent<MeshRenderer>();
                 if(selectionRenderer != null && selectionRenderer.material == defaultRed){
                     selectionRenderer.material = highlightedRed;
                 }
                 else if(selectionRenderer != null && selectionRenderer.material == defaultBlue){
                     selectionRenderer.material = highlightedBlue;
                 }
                 _selection = selection;
             } 
         }
     }
 }