You're talking about Lebanese Zaatar which is red and made with sumac. Everything Lebanese is very very different then the rest of Arabic cuisine - being Palestinian, I enjoy Lebanese cooking, but I prefer traditional Arabic food.
If you want to purchase a good Palestinian version of Zaatar head over to Nassar's where you can buy the proper blend of thyme, thyme, oregano, marjoram, with toasted sesame seeds, and salt.
Get a good olive oil and dip your bread in it with the zaatar.
It's so unbelievably good!