We can see dark blue powder with our naked eyes.It is water-fast. It is absolute a natural pigment abstracted from the leaves of Polygomum tinctorium Lour e.g. blue Polygonum,blue tea, Strobilanthes cusia, woad by modern biotechnology.Widely used in every kinds of textile dyeing as blue coloring.Indigo is very popular with people for thousands of years as the rich color and the fastness.
indigo 
