Did you know all teas come from the same tea plant (Camellia Sinenses) and the way the leaves are processed and oxidized is what makes the variety? Most people have heard of green and black but what about oolong?
Black teas are fully oxidized (exposed to heat and mechanical pressure by either machine or by hand rolling), hence their black color.
Green teas are the least oxidized and that’s how they retain their natural green leaf color.
In between you have your oolong teas, which are only partially oxidized. This variety can vary quite a bit and be greener or darker depending on their specific degree of oxidation.