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Permanent haircolor works through oxidative dye precursors, often called preliminary or aniline derivative molecules. In their small, colorless state, these molecules penetrate the cuticle into the cortex. When mixed with developer, they oxidize and combine into larger color molecules that are trapped within the hair shaft, forming the new color. The earliest stage involves preliminary pigments, which gradually build into the final shade. Base color refers to the background tone in formulation. Contributing pigment refers to the natural underlying pigment exposed during lightening. Toners are separate formulas applied to refine or neutralize tones. Understanding how oxidative dye precursors function is crucial for accurate formulation, gray coverage, and correction services. Proper timing ensures molecules fully oxidize for durability; under-processing leads to fading, while over-processing risks damage. This chemistry knowledge anchors safe and predictable results in professional haircolor services.