For green tea, the tea leaves are harvested from the Camellia sinensis(Plucked and processed on the same day) plant and are then quickly heated—by pan firing or steaming—and dried to prevent too much oxidation from occurring that would turn the green leaves brown and alter their fresh-picked flavor.
A brewed green tea is typically green, yellow or light brown in color, and its flavor profile can range from grass-like and toasted (pan fired) to vegetal, sweet and seaweed-like (steamed). If brewed correctly, most green tea should be quite light in color and only mildly astringent.
By contrast, black tea leaves are harvested and allowed to fully oxidize before they are heat-processed and dried. During oxidation, oxygen interacts with the tea plant’s cell walls, turning the leaves the rich dark brown to black color that black tea is famous for, and significantly altering their flavor profile.
A brewed black tea can range in color from amber to red to dark brown, and its flavor profile can be anywhere from malty to fruity to roasted, depending on how it was processed. Black tea typically has more astringency and bitterness, but if brewed correctly it should be smooth and flavorful.