All true teas - black, oolong, green and white - come from an evergreen shrub called Camellia Sinensis. Its flavors vary because of where the tea is grown and how it's processed. Black tea is a variety that has undergone the longest oxidization or fermentation process over heat than the green, oolong and white tea varieties before it is dried. The result is a rich, stronger flavor, dark brown color with a slight reddish tinge. Its flavors vary depending where the tea is grown and how it is processed. Black teas contain the highest levels of caffeine per cup.