Final answer:
Dark hair goes through one stage of lightening or decolorization. Lightening is achieved through the process of bleaching, which permanently removes the natural pigment of the hair.
Step-by-step explanation:
Dark hair goes through one stage of lightening or one degree of decolorization.
Hair color is determined by the amount and type of melanin present. Dark hair has more eumelanin, which makes it appear darker. Lightening or decolorization is achieved through a chemical process called bleaching, which removes the natural pigment from the hair shaft.
It's important to note that bleaching is a permanent process because it permanently removes the natural pigment. Once the hair has been lightened, it cannot be returned to its original color without the use of hair dye.