Light to medium light hair, i.e. white, gray, and blonde hair to medium blonde hair, can develop green or blue tones when choosing to dye with shades that do not contain any red or with dark colors.
This applies to all herbal hair dyes regardless of brand.
Shades that do not contain red include, for example, black, indigo, and dark brown. Some dark brown shades contain red but are so dark (contain a high proportion of "dark herbs") that they can still cause green/blue tones in the hair.
Therefore, I generally say this applies to ALL dark shades.
Why does hair turn green?
This happens due to the absence of red pigments in the hair from the start. If you have a hair color completely without red pigments, your hair will turn green or have blue tones when dyed with dark shades.
Many blondes and medium blondes have very little red in their hair without it looking red. It rather looks golden blonde/brown. Therefore, they can dye with dark brown shades and still get a nice result.
What can you do about it?
Look at the color wheel. Red is the complementary color to green. Therefore, you need to add red to cancel out the green.
If you have accidentally dyed your hair and it has turned completely green, you can remove the green by dyeing with a shade that contains red. Choose a pre-mixed shade, e.g., brown-red, or mix in some red into your hair dye yourself.
The greener your hair has become, the more red is needed.
Do a test strand at the nape if you are unsure whether your hair contains red or not.
If it turns green, you need to mix in some red in the dye. Experiment with the amounts, but 1 tablespoon of red dye may be enough if you mix it with a (light) brown shade.
If you want to mix with a dark brown or black shade, a much larger proportion of red is required. Always do a test strand until you get the desired color result.
If you absolutely do not want red in the color result, you need to do a 2-step coloring process as Khadi nicely shows on their color chart.
This means you first dye the hair completely red and then dye with your dark hair color. This gives a fully covered dark result without red in it.
The 2-step coloring is the safest way to get a good result without having to experiment with the amount of red in your hair dye.
Feel free to read my other blog article here on how to dye your hair with herbal hair dye in the best way!
Other factors that can cause green hair
There are other factors that can cause green hair. High levels of chlorine in swimming pools can cause green hair in light-haired people. This also applies to those who bleach their hair.
Water from houses with new copper pipes can also cause green hair in light-haired people in connection with dyeing with herbal hair dyes. I know there are skilled hairdressers who can remove both chlorine and copper from the hair.
However, I do not know if the green caused by copper or chlorine can be removed by applying a red herbal hair dye. Maybe someone knows?
