Many types of herbal, black and even green tea can stain teeth and gums. This is because the same is rich in tannins. However, using green tea means that you have a dull grey stain while black one often leaves a yellowish tone. Similarly, herbal ones like chamomile or hibiscus can contribute to staining and discolouration especially if consumed over time.
To avoid these brown stains on your teeth, you do not have to stop the tea intake but need to limit it. For instance - adding milk to the tea or drinking using a straw can help you a lot. You can also opt to steep your tea for a little less time to lighten up a bit.