For light colored hair such as light brown to a normal dark brown you can use a 20.
Hair color developer 20 vs 30.
Works similarly to a volume 20 developer except it lifts a hair starting color by 2 3 levels and works best when a desired color is not more than 2 levels lighter than the existing hair shade.
The 30 volume developer also works like 20 volume but it will lighten the hair s original color by two to three and is more efficient when the desired color is no more than two levels lighter than the original color.
Choose a 30 volume developer when you want a developer that is stronger for a lighter and deeper color.
But if your hair is a very dark brown that looks almost close to black you would use a 30 or maybe even a 40 if.
Benefits of hair developer.
30 volume 9 developer.
Activation hair.
Also you d use it to stay anywhere around the level your hair already is or to lift 1 2 levels.
First off it is optimal for covering grey hair.
Without the developer you would never achieve a significant changes in the color of your hair.
You could upgrade to volume 30 to change your color 3 to 4 shades but keep in mind it can damage thin or fine hair.
20 volume developer 20v 6 peroxide is the most commonly used.
Mixing ratio is usually 1 1 1 1 5 or 1 2 for an extra strong lightening effect.