Can you change GUI Crosshair colour with OnMouseOver rather than Raycasting

First of all I am very new to C# (actually any coding) and am learning on the go for a project. Im trying to make a crosshair that turns red when you are close since I have limited the distance at w$$anonymous$$ch the object interaction works, I want a GUI change to tell you that you are close enough to use the object. All I get is the "NullReferenceException: Object reference not set to an instance of an object" error for the Crosshair script.

here is the mouseover script w$$anonymous$$ch checks distance to player from the object.

 public class Mouseoverbool : MonoBehaviour
 {
     public bool mouseover;
     private checkplayerdist playerDistScript;
     
     void Start()
         {
         playerDistScript = GetComponent<checkplayerdist>();
         }
     
     void OnMouseOver()
     {
     if(playerDistScript.playerclose)
         {
             mouseover = true;
         }
     }
 }

and the crosshair script thats causing the problem

 ublic class CrosshairGUI : MonoBehaviour
 {
     private Color colour;
     private Mouseoverbool islooking;
     
     void OnGUI()
         {
         GUI.color = colour;
         GUI.Label (new Rect(Screen.width/2,Screen.height/2, 50, 50), "X");
         }
     
 
      
     void Start()
         {
         islooking = GetComponent<Mouseoverbool>();
         }
     
     void Update()
     {
         if(islooking.mouseover)
         {
             colour = Color.red;
         }
         else
         {
             colour = Color.w$$anonymous$$te;
         }
         
     }
 }