GameUI.cs

using UnityEngine;
using UnityEngine.UI;
using System.Collections;

public class GameUI : MonoBehaviour 
{
	public Image fadePlane;
	public GameObject gameOverUI;
	
	void Start () {
		FindObjectOfType<Player>().OnDeath += OnGameOver;
	}
	
	void OnGameOver()
	{
		StartCoroutine(Fade(Color.clear, Color.black, 1));
		gameOverUI.SetActive(true);
	}
	
	IEnumerator Fade(Color from, Color to, float time)
	{
		var speed = 1 / time;
		var percent = 0f;
		
		while (percent < 1)
		{
			percent += Time.deltaTime * speed;
			fadePlane.color = Color.Lerp(from, to, percent);
			yield return null;
		}
	}
	
	// UI Input
	public void StartNewGame()
	{
		Application.LoadLevel("Game");
	}
}