There are over 2,000 varieties of the tea plant, grouped into three categories based on how they are processed: black, oolong, and green. Black tea has been fermented and develops an amber-colored, full-bodied brew. Oolong undergoes only a breif fermentation and is therfore paler and more delicate. Green has not been allowed to ferment and produces a yellow-green color. Earl Grey tea was named for Charles Grey, a prime minister to King William IV in the early 19th century; and is a a mixture of Indian and Sri Lankan teas, with flavor from oil of bergamot. In addition there are many other herbal blends (including hibiscus, jasmine, hawthorn, and chamomiles) which add their own distinctive flavors but are not actual teas.
The leaf size and type of tea will determine the brewing time: 1-2 min for green, 3-5 min for full-leaf black, and 7-10 for small-leaf oolong. Brewing past these prime ranges will cause the tea to turn bitter and pungent, which is why you should immediately remove tea from the liquid. You should always judge a tea by taste, not color.