simple camera fade script

CameraFader.cs

using UnityEngine;
using System.Collections;

public class CameraFader : MonoBehaviour {

  public delegate void endFunction();
	public endFunction endCall;
	
	Texture2D blackTex;
	
	public bool fadeout = false;
	public float delay = 0.0f;
	float startTime = 0f;
	Color color = new Color(1f,1f,1f,0);
	
	bool  needDestroy = false; //used for delay destroy, as fadeout then fadein screen flashing

  float _duration = 1f;
	public float duration {
		set {
			_duration = value;
		}
		get {
			return _duration;	
		}
	}
	
	float elapseNormlized {
		get {
#if UNITY_EDITOR
			float norm = (Time.time - startTime ) / _duration;
#else 
			float norm = (Time.realtimeSinceStartup - startTime ) / _duration;
#endif
			return norm;
		}
	}
	
	public float target {
		get {
			return fadeout ? 1.0f : 0f;	
		}
	}

	void Awake() 
	{
#if UNITY_EDITOR
		startTime = Time.time + delay;
#else
		startTime = Time.realtimeSinceStartup + delay;
#endif
		blackTex = new Texture2D(1,1,TextureFormat.ARGB32,false);
		Color[] colors = new Color[1];
		for (int i = 0; i < colors.Length; i++) {
			colors[i]=Color.black;
		}
		blackTex.SetPixels(colors);
		blackTex.Apply();
		
	}
	
	void Update() {
		if(needDestroy) {
			Destroy(gameObject);
			return;
		}
		float current = 0;
		float norm = elapseNormlized;
		if(norm > 1.0f) {
			if(endCall != null) endCall();
			needDestroy = true;
			return;
		}
		
		if(fadeout) {
			current = Mathf.Lerp(0f, 1f, norm);
		}
		else {
			current = Mathf.Lerp(1f, 0f, norm);
		}
		
		color.a = current;	
	}
	
	void OnGUI () 
	{
		if(Event.current.type != Event.repaint) return;
#if UNITY_EDITOR
		if(Time.time < startTime ) return;
#else 
		if(Time.realtimeSinceStartup < startTime) return;
#endif
		Color c = GUI.color;
		GUI.color = color;
		int depth = GUI.depth;
		GUI.depth = -10;
		GUI.DrawTexture(new Rect(0,0, Screen.width, Screen.height), blackTex);
		GUI.depth = depth;
		GUI.color = c;
	}
	
	public static CameraFader NewFadeIn(float duration = 1f, float delay = 0.0f)
	{
		GameObject go = new GameObject("CameraFader");
		DontDestroyOnLoad(go);
		CameraFader fader = go.AddComponent<CameraFader>();
		fader.fadeout = false;
		fader.duration = duration;
		fader.delay = delay;
		return fader;
	}
	
	public static CameraFader NewFadeOut(float duration = 1f, float delay = 0.0f) {
		GameObject go = new GameObject("CameraFader");
		DontDestroyOnLoad(go);
		CameraFader fader = go.AddComponent<CameraFader>();
		fader.fadeout = true;
		fader.duration = duration;
		fader.delay = delay;
		return fader;
	}
}

CamerFaderTest.cs

using UnityEngine;
using System.Collections;

public class CameraFaderTest : MonoBehaviour {
  
  void Start(){
     //level 1 enter fade in 
    CameraFader.NewFadeIn().endCall = delegate {
      //finish level1
     //level 1 fade out
  		CameraFader.NewFadeOut().endCall = delegate {
        //load level2
        //and then fade in level2
				CameraFader.NewFadeIn();
			};
		};
}