Indigo is the colour which has seduced the world for centuries. The dye is extracted from a plant Indigofera tinctoria and related species. India grew indigo ever since the Indus Valley civilization, 2000 BC. The pigment was an important part of the cargo on the Caravelas, sailing to the west through the blue waters of the Indian Ocean. I covered some rocks on the seaside in Goa with indigo during the low tide and waited for the high tide to rise and wipe off the pigment.