Oolong tea (Chinese for Black Dragon) is a half fermented tea. The leaves are first withered in the sun, just like in manufacturing of black tea, but for a shorter period of time: only about 4-5 hours. When the leaves are about half fermented, they are fired to stop the fermentation process. Oolong teas are usually dark green or reddish brown.

What's brown and sounds like a bell?

Oolong.