Indigo refers both to the blue pigment used as a dye and to indigo plants of the genus Indigofera. Indigo dye has been used for thousands of years by civilizations all over the world to dye fabric blue. It has been the most famous and most widely used natural dye throughout history and is still extremely popular today as evidenced by the familiar colour of blue jeans.
For experienced dyers as vatting is required.
It is the only dye in the world that starts blue, turns yellow, changes to green, and then finally transforms itself again to true blue.