Change parent material on press K c# unity.

I want to change material while pressing the button but it does not work for me.

The code is on the child

Code (CSharp):

1. public Material Mat;
2.     void Update () {
3.         if (Input.GetKeyDown(KeyCode.K))
4.         {
5.             transform.parent.GetComponent<Renderer>().material = Mat;
6.         }
7.     }

 

does something like this work? just for testing.
transform.parent.GetComponent<Renderer>().material.color = Color.red;

 

What exactly mean that "it doesn't work"? Do you have error messages in the console? It just does not updates the material? How do you know that? Are you sure it does not update the material?