Rooibos is not widespread, and seems to only be grown in the region of Western Cape Province of South Africa. Generally speaking, the leaves go through a process of oxidation and produces the distinctive reddish brown color we see in rooibos teas. It enhances the flavor.
If leaves are unoxidized, they are referred to as "green" rooibos. There is a more demanding production process for green rooibos and it makes it more expensive than the traditional rooibos. (It is a method similar to one that produces green tea) The green rooibos has a more malty flavour.
Rooibos is Afrikaans for red bush, and is a member of the legumes family of plants. It has been popular in Africa for a long time, and is now being consumed more around the world.