camera.clearFlags = CameraClearFlags.SolidColor;

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
void Awake() {
camera.clearFlags = CameraClearFlags.SolidColor;
}
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

def Awake():
camera.clearFlags = CameraClearFlags.SolidColor