Indigo. According to the word knowledge of indigo, we know that it is fiery red, green, golden and indigo. Indigo is another name for indigo, a liquid made by soaking indigo grass, also refers to dark blue; indigo, an organic dye dark blue, is made by fermenting indigo indigo and leaves of plants containing indoleic acid such as woad, wood indigo, and horse indigo. Indigo can also be synthesized artificially (ancient books say: all five kinds of blue can be indigo - Song Yingxing). It is used to dye cloth with a long-lasting color, commonly known as indigo, and in some areas it is called indigo.