True blue blooms, as gardeners know, are hard to find. No less for our ancestors searching for such a source to dye both textiles and themselves.
A reliable blue was discovered at least 6,000 years ago, in various species of Indigofera, a genus of some 700 species of leguminous annual and perennial herbs, shrubs and small trees native to tropical and warm regions. The major natural dye source has been I. tinctoria, a deciduous subshrub with pink and blue flowers originating in southeast Asia.
