Raycast pink material

Hi all, i'm a beginner with Unity and I have a problem with RayCast. My objective is to make a chess board, and to change the color of the square I click on, the selection is correct (the correct square change color), but it become pink. Here is my full code (the raycast is at line 31) :

 using UnityEngine;
 using System.Collections;
 
 public class Modele : MonoBehaviour {
     
     public Material mat;
     
     // Use this for initialization
     void Start () {
         GameObject caseC, caseF;
         caseC = GameObject.Find("CaseC");
         caseF = GameObject.Find("CaseF");
         GameObject tmp = null;
         for(int i=0 ; i<8 ; i++) {
             for(int j=0 ; j<8 ; j++) {
                 if(i%2 == j%2)
                     tmp = (GameObject)Instantiate(caseC);
                 else
                     tmp = (GameObject)Instantiate(caseF);
                 tmp.transform.position = new Vector3(i,0,j);
             }
         }
         Destroy(caseC);
         Destroy(caseF);
         select = null;
     }
     
     // Update is called once per frame
     void Update () {
         if (Input.GetMouseButtonDown(0)){ // if left button pressed...
             Ray ray = camera.ScreenPointToRay(Input.mousePosition);
             RaycastHit hit;
             if (Physics.Raycast(ray, out hit)){
                 hit.collider.gameObject.renderer.material = mat;
             }
         }
     }
 }
 

http://image.noelshack.com/fichiers/2014/51/1418648844-sans-titre.jpg

As you can see in the screen, my public variable is set. I also tried to do it with the texture directly (with a Texture variable and with the material.mainTexture attribute), but it make the area white.

An other small question would be : what is the better way to create 64 squares, I don't think my method is really good...

Sorry for my English, It's not my native language, and thank you for your time.