Indigo: Explained For most of us, the first time we would have learned about indigo would have been in school, when we were taught color theory and the acronym for the colors of the rainbow: ROYGBIV.

In a thirty- year period, indigo planters doubled their profits every three to four years, and on the eve of the American Revolution, when cubes of indigo replaced paper currency, South Carolina ...

While indigo traces its roots to India, the African slave trade made it exceedingly valuable on that continent. "Indigo was more powerful than the gun," McKinley tells Tell Me More host Michel Martin.