Indigo
A deep blue dye from the leaves of the indigo plant, and the colour it gives.
Also: neel, nil
Indigo is the blue of denim. The dye comes from the leaves of plants of the genus Indigofera, grown and processed in India for thousands of years; the word itself comes from the Greek for Indian. The leaves are fermented to release the dye, which is dried into cakes. Cloth dipped in an indigo vat comes out yellow-green and turns blue in the air. Under British rule, forced indigo growing in Bengal and Bihar led to revolts, and to an early campaign by Gandhi at Champaran in 1917. Synthetic indigo, sold from the 1890s, replaced most of the plant crop.