Short answers, pulled from the story.
Indigofera tinctoria, also called true indigo, is a shrub in the bean family that grows 1-2 meters tall. Its native range spans tropical West Africa, Tanzania to South Africa, and the Indian subcontinent to mainland Southeast Asia.
Leaves of Indigofera tinctoria were soaked in water and fermented to convert the natural glycoside indican into the blue dye indigotin. The fermented solution was then mixed with a strong base such as lye, causing the dye to precipitate out.
Natural indigo from Indigofera tinctoria is called tarum in Indonesia and nila in Malaysia. In Iran and parts of the former Soviet Union it is known as basma.
Marco Polo, writing in the thirteenth century, was the first European to report on the preparation of indigo in India.
Because it is a legume, Indigofera tinctoria is rotated into fields to improve soil fertility, in the same way as alfalfa and beans. It is also grown widely as a soil-improving groundcover.
Most indigo dye today is synthetic, but natural dye from Indigofera tinctoria is still produced and sold, marketed as a natural colorant. It has been used in European easel painting since the Middle Ages.