I knew a bit about indigo — but not that in addition to the Old World’s Indigofera tinctoria there’s a separate species in the same genus that was used in ancient America for making dye. I found out because of some interesting detective work on the Maya pigment. I figured that the indigo plant mentioned in the research was something completely different, but it turns out to be I. suffruticosa. Although there do seem to be other genera that produce the colour.