Camera.backgroundColor

Description

The color with which the screen will be cleared.

Only used if clearFlags are set to CameraClearFlags.SolidColor (or CameraClearFlags.Skybox but the skybox is not set up).

// ping-pong animate background color
using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour
{
    public Color color1 = Color.red;
    public Color color2 = Color.blue;
    public float duration = 3.0F;

    public Camera cam;

    void Start()
    {
        cam = GetComponent<Camera>();
        cam.clearFlags = CameraClearFlags.SolidColor;
    }

    void Update()
    {
        float t = Mathf.PingPong(Time.time, duration) / duration;
        cam.backgroundColor = Color.Lerp(color1, color2, t);
    }
}

Additional resources: camera component, Camera.clearFlags