If in Unity Play Mode, parses through a series of objects and assigns a material to them (to let them stand out in the scene).

PlayModeDetector.cs

using UnityEngine;
using System.Collections;

namespace TheBitCave {

	public class PlayModeDetector : MonoBehaviour {

		public Material material;
		public GameObject[] gameObjects;

		void Start () {
			if(Application.isPlaying && Application.isEditor) {
				foreach(GameObject go in gameObjects) {
					if(go.GetComponent<Renderer>() != null)
						go.GetComponent<Renderer>().material = material;
				}		
			}
		}
		
	}
}