Anil is a natural dye derived from the indigo plant, which is used to produce a deep blue color. It has been used for centuries in many cultures, and is still used today in clothing, fabrics, and other products. The dye is made by fermenting the leaves of the indigo plant, and then extracting the pigment. The pigment is then mixed with a mordant, such as alum, to create a dye that can be used to color fabrics.