It may sound a bit odd but your hair is a mixture of 3 colors; red, yellow, and blue. These are the primary colors. Secondary colors are orange, green, and violet. If you look at the "wheel" a color opposite (directly across) will "negate" that color.
This means if your hair is an orange color - blue will make it a brown/black color. If you hair has a yellow tone, violet will cancel it out.
One of the most important elements of hair coloring is determining the hairs' "underlying pigment" (the hairs' natural color.) When you chose a color in a swatch book, your hair may not come out that color because of the underlying pigment in your hair.
Underlying color + Artificial color = Final result
While “color” refers to the hairs’ underlying pigment, “level” is the lightness or darkness of the hair. It ranges from level 1 (darkest) to level 10 (lightest). Together, color and level form your hair color. For example, you could be a level 3 Gold (Dark Golden Brown) and your friend a level 3 Red (Dark Red). You would both be the same level of darkness but your colors will look very different on each. The same goes for levels; a level 6 Ash (Light Ash Brown) will look very different from a level 10 Ash (Light Ash Blonde).
Think of it as an algebraic equation: Level + Color = Hair Color
1=Black
2=Very Dark Brown
3=Dark Brown
4=Brown
5=Medium Brown
6=Light Brown
7=Dark Blonde
8=Light Blonde
9=Very Light Blonde
10=Light Platinum Blonde
Before any permanent color can be deposited into the hair shaft, the cuticle, or outer layer, must be opened.
The insoluble formula then reacts with the cortex, or middle layer, to deposit or remove the color. The color is available in a variety of forms: creams, gels or tubes, or shampoos.
These will not permanently change the hair color until they are part of an oxidation chemical reaction.
The Oxidizing Agent or Developer is hydrogen peroxide in one of various forms and strengths. lt is the catalyst or cause of the chemical reaction which allows the formula to permanently alter the hair's color. The strength of the developer - is determined by the desired results directions.
Too much developer and the color may not have good highlights, cover poorly, not lift to the correct level and fade more quickly.