How can I paint a picture and then compare it to another?

I want to make the game similar to ink.inc . Right now I'm trying to make the core gameplay of the game. There is an example image and I should try to paint as precise as I can and then compare them. Right now I found 2 separate solutions on the internet: One for painting and saving the texture and one for comparing textures. The first one is from a youtube tutorial: https://www.youtube.com/watch?v=DCD8Pt1zf4c The code from this video:

 using System.Collections;
 using System.IO;
 using UnityEngine;
 
 public class Paintable : MonoBehaviour {
 
     public GameObject Brush;
     public float BrushSize = 0.1f;
     public RenderTexture RTexture;
 
     // Use this for initialization
     void Start () {
         
     }
     
     // Update is called once per frame
     void Update () {
 
         if (Input.GetMouseButton(0))
         {
             //cast a ray to the plane
             var Ray = Camera.main.ScreenPointToRay(Input.mousePosition);
             RaycastHit hit;
             if(Physics.Raycast(Ray, out hit))
             {
                 //instanciate a brush
                 var go = Instantiate(Brush, hit.point + Vector3.up * 0.1f, Quaternion.identity, transform);
                 go.transform.localScale = Vector3.one * BrushSize;
             }
 
         }
     }
 
     public void Save()
     {
         StartCoroutine(CoSave());
     }
 
     private IEnumerator CoSave()
     {
         //wait for rendering
         yield return new WaitForEndOfFrame();
         Debug.Log(Application.dataPath + "/savedImage.png");
 
         //set active texture
         RenderTexture.active = RTexture;
 
         //convert rendering texture to texture2D
         var texture2D = new Texture2D(RTexture.width, RTexture.height);
         texture2D.ReadPixels(new Rect(0, 0, RTexture.width, RTexture.height), 0, 0);
         texture2D.Apply();
 
         //write data to file
         var data = texture2D.EncodeToPNG();
         File.WriteAllBytes(Application.dataPath + "/savedImage.png", data);
 
 
     }
 }

The second with this code from StackOverflow answer:

 private bool CompareTexture (Texture2D first, Texture2D second)
 {
     Color[] firstPix = first.GetPixels();
     Color[] secondPix = second.GetPixels();
     if (firstPix.Length!= secondPix.Length)
     {
         return false;
     }
     for (int i= 0;i < firstPix.Length;i++)
     {
         if (firstPix[i] != secondPix[i])
         {
             return false;
         }
     }
 
     return true;
 }

The problems that I currently have are the following:

1) While painting the tutorial way the output looks weird and colors are not exact as in a play mode.

In unity the painted picture looks like this: https://prnt.sc/qacd16

If you open it in finder it looks like this: https://prnt.sc/qacel5

How can I make it look the same as in Unity?

2) Because of the lighting and other stuff, the colors are obscured ob the painted image and as a result, I can't compare these images with the original one.

Would be grateful for any help :)