How to randomly chenge camerabackground color every 5 seconds?

I want to change camera background color randomly from 50 to 200 every 5 seconds. How to do that?
i am using below scrip but its not working.

public class Camera_cript : MonoBehaviour {
Color bgcolor = Color.white;
Color current = Color.black;
Camera camera;
public float duration = 3.0F;

// Use this for initialization
void Start () 
{
	camera = GetComponent<Camera> ();

}

void Update () 
{
	float t = Mathf.PingPong(Time.time, duration) / duration;
	camera.backgroundColor = Color.Lerp(current,bgcolor,0.5f);
}

}

Have you set camera clearFlags ?

Add this line of code in Start() :

camera.clearFlags = CameraClearFlags.SolidColor;

For every 5 seconds :

private float nextActionTime = 0.0f; public float period = 0.1f;

void Update () 
{ 
     if (Time.time > nextActionTime ) 
     { 
           nextActionTime = Time.time + period; 
          // execute block of code here 
     } 
}