The precise identification of this natural dye is a little unclear. We found two somewhat different takes on this pigment code. From Artiscreation we found that Myrobalan is a dye that is used in India. It is made from the Terminalia chebula fruits. It is used as a mordant as well as a dye and produces a yellowish color.
Interestingly, Kremer pigments lists their Oak Apples as NBr6. As far as we can tell these are different substances. Oak galls have some things in common with Myrobalan, such as high levels of tannin, but they are different. Regard oak gall, Kremer's information states, "The best quality Aleppo galls collected in Turkey, known as "blue\“ or "green galls", are hard and heavy and of dark bluish-green or olive green color. They contain up to 70 % of gallotannic acid." More can be found here. Oak apples are also called gallnuts and are related to the production of Iron Gall ink, which was used in Old Masters drawings.
