Indigo has been used to dye fabrics for millennia: the oldest evidence of its use dates back to 6,000 years ago in Huaca Prieta, Peru, but it was used in Mesopotamia, ancient Egypt, Mesoamerica and Africa, in addition to India, Japan and Southeast Asia.
Although it is a dye that is widespread throughout the planet, there are different types of plants that give us that wonderful blue: Isatis, Persicaria, Wrightia and Strobilantthes.
I am growing two species of indigo: Persicaria tinctoria and Isatis tinctoria.