Indigo is made by grinding the leaves of indigo plant. This dye is safe for dying hair . This powder is mixed with henna powder for coloring hair dark.It cover grey hair . Depends on the darkness of hair you need, quantity can be increased with henna powder . For dark color, henna can be 2 tbsp and indigo can be 3 to 4 tbsp.Indigo can be used after one day of henna application in the hair.