unityengine.component does not contain definition

I am receiving an error telling me that unityengine.component does not contain a definition for “material”

here is my code;

using UnityEngine;
using System.Collections;

public class TileMouseOver : MonoBehaviour {
	
	// Update is called once per frame
	void Update () {
	
	}

	void OnMouseOver() {
		renderer.material.color = Color.blue;
	}

}

What version of unity do you use?
If you are using unity 5 you need to use the GetComponent function to get your render since unity remove the shortcut version.

GetComponent<Renderer> ().material.color = Color.blue;

If that does not solve the problem can you post the whole error massage?