For making indigo oil indigo leaves powder amla powder and bhringraj powder shall be boiled together in a pan till the water evaporates and the sizzling sound stops. These 3 herbs also forms the base for the famous neelibhrigraj oil which is very popular. For dyeing if you want black color make sure to use it after applying henna this will ensure you get a dark color. If you want a dark reddish tinge color you can mix both henna and indigo together and apply. Side effects of indigo powder: There are no side effects to using indigo powder for hair.