Indigo was originally made from two plants. One is Woad, Isatis tinctoria, a native of Greece and Italy, and the other is Indigo, Indigofera tinctoria, a native of India.
At the end of the 19th century, German scientists synthesized the dye, and production from plant sources declined. Most of the dye today comes from China.
Recently, bacteria have been genetically engineered to produce the dye.
Other closely related dyes are erioglaucine, known as FD&C blue #1:
FD&C Blue #1: Erioglaucine
and Fast Green, FD&C green #3:
FD&C Green #3: Fast Green
Indigo is the dye used to color blue jeans. It is also used in foods under the name FD&C Blue #2.