In Unity, how do I make a mesh change its opacity during runtime?

Question

I'm trying to make a isometric game. I want to make it so that when the player goes behind a wall, the wall's alpha goes down.

How do I go about doing this?

I have this code that I made, but I don't understand what's wrong with it.

I already have the wall that's meant to disappear on the "Wall" layer.

using UnityEngine;
using System.Collections;

public class WallAlpha : MonoBehaviour {

    public LayerMask mask =LayerMask.GetMask("Wall");

    void Update() {

        if (Physics.Raycast(transform.position, transform.forward, 100, mask.value))
        {
            transform.GetComponent<Renderer>().material.SetColor("_Color", new Color(1,1,1,0.1f));
            Debug.Log("Something in the way");
        }

        else
        {
            transform.GetComponent<Renderer>().material.SetColor("_Color", new Color(1,1,1,1.0f));
            Debug.Log("Nothing In the Way!");
        }
    }
}

Answer 1

Actually Unity create a default material for meshes if you don't assign any material explicitly. And the Rendering Mode of that default material is set to Opaque that prevents you to play with transparency. Although _Color property is declared in Standard Shader. Means your code is right. Well, it's totally another topic. What you can do is to create your own material, set its Rendering Mode to Transparent and drop it on your mesh.

1- Create a New Material.

2- Set it's Rendering Mode to Transparent.

3- Drop that material on your mesh.

Now you can play with transparency.