Tea leaf egg or simply tea egg is a typical Chinese savory food, commonly sold as a snack. The eggs are boiled with spices and, of course, with red/black tea, hence the name tea eggs.
I followed mainly the first video below, although I used a regular stove pot instead of a rice cooker, 5-spice instead of those ingredients and tea bags instead of tea leaves in the video. After soaking overnight in the tea liquid, the eggs were imprinted with very nice looking marble patterns. The eggs were very tasty as well.