Fader.cs

using UnityEngine;
using System.Collections;

public class Fader : MonoBehaviour {

	public Texture2D fadeoutTeture;
	public float fadeSpeed = 2f;


	int drawDepth = -1000;
	private float alpha = 1.0f;
	private int fadeDir = -1;

	void OnGUI ()
	{
		alpha += fadeDir * fadeSpeed * Time.deltaTime;

		Mathf.Clamp01 (alpha);

		GUI.color = new Color (GUI.color.r, GUI.color.g,GUI.color.b,alpha);
		GUI.depth = drawDepth;
		GUI.DrawTexture(new Rect (0, 0, Screen.width, Screen.height), fadeoutTeture);
	}

	public float BeginFade (int direction)
	{
		fadeDir = direction;
		return (fadeSpeed);
	}

	void OnLevelWasLoaded ()
	{
		BeginFade (-1);
	}
}