What makes tea, a tea? We'll take the grey out of the discussion and keep it simple. :)
The Plant: Camellia sinensis
All teas come from the same species of plant. Camillia sinensis is a shrub or small tree that originated from East Asia. The species is part of the genus Camellia, and sinensis comes from Latin to mean "from China". The leaves, and in some cases twigs, harvested from the plant are what we use to make tea.
Often times, particularly in the West, herbal blends not from Camillia sinensis are incorrectly referred to as "tea". Chamomile, hibiscus, and peppermint, to name a few, are botanical ingredients used in drinks. However, these botanical blends are not technically "tea".
Oxidation
Though all from the same species of plant, we get different varieties of teas by varying the level of oxidation in the leaves. Oxidation is a chemical reaction which tea producers control by using special methods to initiate, stop, or prevent oxidation depending on the type of tea being produced. During oxidation, polyphenols known as catechins are converted into other types of polyphenols known as flavanoids. Two types of flavanoids, theaflavins and thearubigins, give the leaves different color and flavor.
Color-Oxidation Spectrum
Green tea is made from leaves that have undergone little to no oxidation. Black tea, on the other hand, is made from leaves that have experienced almost full oxidation. If you think of a spectrum where green tea (no oxidation) is on one end and black tea (full oxidation) on the other, oolongs would fall anywhere along the spectrum between the two. As one might imagine, oolongs can vary significantly in color and flavor.
White tea is made from young leaves, and sometimes buds, from the same Camillia sinensis species of shrub. The name comes from the tiny, white hairs that often cover the leaves.
Rare Color Varieties
There are other, rarer varietals of tea. Yellow tea leaves come exclusively from China and are generated using a slow oxidation process. Yellow tea is often enjoyed by those who wish to enjoy the health benefits of green tea but do not like the grassy flavor often associated with green tea.
Purple tea comes from the same Camillia sinensis plant, however a genetic mutation causes the plant to have higher levels of anthocyanin. This antioxidant is the same one that gives blueberries their brilliant blue color and gives the tea leaves a unique purple color. By varying the oxidation of the purple tea leaves, producers can make green, oolong, and black varietals of purple tea.
So there you have it - a rainbow of tea flavors. We challenge you to try a few, and enjoy!