How to change the camera background colour with player height.

Hey I currently am making a 2D side scroller and I am trying to get my background colour to change to give the effect of flying into space (if they get that high). I have been able to get the background colour of the main camera to change when the player hits a certain height but I can't get the desired effect if the player is falling back to earth.

 using UnityEngine;
 using System.Collections;
 
 public class CameraBackGround : MonoBehaviour {
 
     private GameObject playerMovement;
 
     public Color backgroundSky = Color.blue;
     public Color backgroundSpace = Color.black;
 
     private float transfer = 10f;
     private float deltaTime = 0f;
 
     void Start()
     {
         playerMovement = GameObject.FindGameObjectWithTag("Player");
     }
 
     void Update()
     {
         
         if(playerMovement.transform.position.y >= 10f)
         {
             dayToNight();
         }else if(playerMovement.transform.position.y > 2f && playerMovement.transform.position.y < 10f)
         {
             nightToDay();
         }
         
     }
 
     void dayToNight()
     {
         deltaTime += Time.deltaTime;
         GetComponent<Camera>().backgroundColor = Color.Lerp(backgroundSky, backgroundSpace, deltaTime);
     }
 
     void nightToDay()
     {
         deltaTime += Time.deltaTime;
         GetComponent<Camera>().backgroundColor = Color.Lerp(backgroundSpace, backgroundSky, deltaTime);
     }
 }

Basically if my player reaches a certain height then the transition between the two colours should start but if the player falls back to the ground then I want it to return to the original background colour.