SetPixels PROBLEM (trying to put decals)

Hi, basically I want to put transparent texture onto base texture with SetPixels function. I'm using raycast to get mesh texture coordinates. Please help :) Here is the code:

 using UnityEngine;
 using System.Collections;
 
 public class DecalSystem : MonoBehaviour 
 {
     public Texture2D layerTex;    //Base texture
     public Texture2D decalTex; //Transparent texture
     
     private Camera cam;        //Camera
     private Ray ray;        //Ray
     private RaycastHit hit;//Raycast
 
     void Start()
     {
         cam = Camera.main;
     }
     
     void Update()
     {
         if (!Input.GetMouseButtonDown(0))        
             return;
         
         ray = cam.ScreenPointToRay(Input.mousePosition);
         if(Physics.Raycast(ray, out hit))
         {
             if(hit.collider.name == "Board")
             {
                 Vector2 layerUV = new Vector2(hit.textureCoord.x, hit.textureCoord.y);
                 
                 //// Dont work from here:
                 //    Color[] decalPixels = new Color[decalTex.width * decalTex.height];
                 //    layerTex.SetPixels(layerUV.x, layerUV.y, //DONT KNOW, //DONT KNOW, decalPixels);
                 ////
                     
                 layerTex.Apply();
             }
         }
     }
 }