Parser Error.

using UnityEngine;
using System.Collections;

public class NewBehaviourScript : MonoBehaviour {

	// Use this for initialization
	void Start () {
	
	}
	
	// Update is called once per frame
	void Update () {
	
	}
}

{
void OnMouseEnter()
	{
		renderer.material.color = Color.cyan;
	}

You brackets are in the wrong place:

using UnityEngine;
using System.Collections;

public class NewBehaviourScript : MonoBehaviour {

    // Use this for initialization
    void Start () {

    }

    // Update is called once per frame
    void Update () {

    }



void OnMouseEnter()
    {
       renderer.material.color = Color.cyan;
    }

}