Hair Coloring and Lightening
Language of color
Hair color is described by level (1 black to 10 lightest blonde) and undertone (warm, neutral, cool). The law of color: primary colors (red, yellow, blue) mix to make secondary colors (orange, green, violet), and complementary pairs neutralize each other - blue cancels orange, green cancels red, violet cancels yellow. That is the tool for correcting unwanted warmth.
Products and developers
Temporary color sits on the cuticle; semipermanent deposits without lift; demi-permanent deposits and blends gray with little or no lift; permanent color lifts and deposits through an oxidation reaction with hydrogen peroxide, so it requires a patch test (typically 24 to 48 hours before) and a strand test. Developer volume sets the amount of lift: 10 volume deposits, 20 volume lifts about one to two levels, 30 more, 40 the most. Developer does not choose the shade - the color formula does.
Lighteners and correction
On-the-scalp lighteners are weaker and safer for scalp application; off-the-scalp products, including oil and cream lighteners, are stronger. Apply to mid-lengths and ends last when porosity differs. Fillers add missing pigment before recoloring, and a soap cap can soften a too-dark result.
Traps
Believing more developer always means more lift; skipping a patch test because the client used the product before; forgetting that lightened hair is more porous and grabs tone; applying permanent color over a fresh relaxer.
Rule of thumb
With 20 volume at a one-to-one ratio, expect roughly one to two levels of lift; if the goal needs more, change the lightener rather than the processing clock, and always strand test porous hair.