The breakfast teas "Earl Grey" and "Lady Grey" contain Bergamot oil. Bergamot oil comes from the Bergamot orange, an Italian variety grown solely for its extract - the fruit body is not usually consumed. It is used to make things flavorful and fragrantful, and I think you'll agree that it does a good job of that.
However, you can not ferment kombucha in teas that contain Bergamot oil - like other essential oils, it is a weak preservative. Kombucha brewed with Earl or Lady Grey tea will result in an incomplete ferment and an enfeebled culture.