ボタンのクリックを押しながら背面をクリックするのを防ぐ

ChangeColor.cs

using UnityEngine;
using System.Collections;
using UnityEngine.EventSystems;

public class ChangeColor : MonoBehaviour {

	MaterialPropertyBlock block;

	void Start()
	{
		block = new MaterialPropertyBlock();
		block.SetColor("_Color", Color.red);
	}

	void OnMouseUp () 
	{
		GetComponent<Renderer>().SetPropertyBlock(null);
	}

	void OnMouseDown()
	{
		if(EventSystem.current.IsPointerOverGameObject()){
			return;
		}
		GetComponent<Renderer>().SetPropertyBlock(block);
	}
}