All plant dyes are naturally vegan hair dyes.  Plant dyes are very different to chemical dyes when trying to achieve varying colours.  It can be done but does require a certain amount of experimental trial and error for each individual hair colour.  When fruit juices containing anthocyanins (pigments that can appear red, purple, blue or black depending on ph levels) are used to mix henna, the dye colour may vary. Antioxidants may also vary colour.

There are many factors to be taken into consideration when using natural hair dye colours (i.e. body temperature, heat) but with frequent use you will get to know what combination suits your individual hair colour. Whatever you do you will never regret using plant dyes such as henna, indigo, cassia, manjistha natural hair dyes.

One thing to remember with natural plant dyes is that you can always dye hair darker but you cannot lighten dark hair colour unless you bleach hair first.

Pure henna powder from the henna plant lawsonia inermis is a natural green powder, well a sort of yellow green colour (cannot be any other colour, if it is, i.e. red, then it is not pure henna and contains chemicals). When the powder is mixed with an acidic liquid it releases an orange red dye ready for use as a hair dye. 

Pure indigo powder from the Indigofera Tinctoria plant is also a natural green powder (any other colour i.e. black, then it contains chemicals). Indigo powder is also known as black henna because it gives off a very dark blue dye when mixed with water and together with henna makes a black hair dye. It is not the commercial black henna which is an instant black colour that does contain chemicals. Indigo must be mixed with henna to get a natural black hair dye.

Indigo by itself can be used on natural existing black hair (with no grays or any other colour) to give depth to black hair and a more blue black colour but never use alone on white or gray hair otherwise you will end up with blue-green hair.

Henna is very dominant and easily overpowers indigo which is weaker as it can can lose dyeing powders easily but together, they can create any hair shades of browns and black.

Henna gives an orange red dye and indigo gives a blue dye and when both are combined in correct proportions can give light, medium or dark brown using a one-step process. To get black hair dye however requires a two-step process of putting henna on first, washing out and then applying indigo. The whole idea being blue over orange/red gives black or jet black. You can get a nearly black using the one-step process by using as much indigo as possible i.e. up to 90-95% indigo to 10% or 5% henna but never black. It just doesn’t work. 

Indigo with amla powder – mix amla powder into indigo powder to keep hair conditioned and soft but do not overpower indigo with amla as indigo is far less dominant than henna and loses dyeing power easily so the resulting color might be different than expected i.e. could end up with dark brown hair as opposed to black if indigo is overpowered as it may weaken dyeing capabilities but can use up to 50% of amla to 100% indigo