Very deep blue fabric, hand-dyed for a very long time in Senegal and elsewhere in Africa and India. The indigo color is obtained from a tree called "the indigo tree". The leaves of the indigot tree are said to have medicinal properties as well.
Washing advice: Take some precautions with this vegetable dye. It takes a first wash before wearing or using an indigo fabric. Rinse your clothing or fabric in a bath of strongly salted water or water to which 1/3 of white vinegar has been added. This action limits the bleeding of colors and fixes them.