Disclaimer: I am full of useless information. This is stuff I have read somewhere and retain in my head for some reason. Use this only to impress your tea drinking friends and not for actual research purposes.
White, green, and black tea. An educated tea drinker knows that all tea comes from the same plant, Camellia sinensis, therefore tea is categorized by the age that the leaf is plucked and the method of controlled chemical reactions (oxidation) that occurs after harvesting. Oxidation is the natural chemical process that occurs if the leaf is not immediately heated to 170*F after picking. It basically means the tea is left to darken and wither. Allowing the leaf to wilt creates a darker cup of tea with higher levels of caffeine (okay, maybe even an educated tea drinker doesn't know all of that). So without getting into too much detail and bringing in a bunch of tea names the general public is not aware of and to keep this from being a boring long post, I'm dividing popular teas into three categories: white, green and black.
White tea is the newest tea on the Western market and is getting some exciting news. It differs from other tea because it is made from the unopened buds of the tea plant. When it is harvested the bud is covered with a fine white fuzz which is why it is known as white tea. The buds are not left to wilt and oxidize but instead are immediately steam dried giving a wonderfully light flavor and richly healthy cup of tea. This variety has very low caffeine (5-10% of coffee) and contains the most anti-oxidents of all teas. It is properly prepared and enjoyed using water just short of boiling.
Green tea is processed identically to the white tea with the age of the tea leaf being the difference. It is dried soon after harvesting. Receiving very little processing creates its characteristic raw and grassy flavor. The caffeine level about 15-20% of coffee. This tea should be made with water that is just short of boiling, as using hotter water will produce a bitter cup of tea.
Black tea is leaves allowed to whither for five hours before being steamed giving you a fully oxidized, dark and bitter cup of tea. It contains about 45% of caffeine as coffee. Black tea should be made with water near the boiling point.
Like I mentioned before, I would be silly to try to categorize all tea into only three categories. There are lesser known varieties such as oolong and pu-erh, medicinal herbal infusions, teas whose flavor vary from the regions that they are produced, and tons more.
I must say that I drink lots of white tea, organic of course, about three cups a day. No sugar, no milk, just hot tea. I love it.
Although while writing this I am drinking a coffee. Ironic?