Which of the following best describes hair lightening?

Hair lightening primarily involves the removal or neutralization of color, which can lead to a lighter appearance of the hair. This process is typically achieved through the use of chemical agents, such as hydrogen peroxide or ammonia, which penetrate the hair shaft and break down the natural pigments, allowing for a lighter shade to be achieved.

In contrast, darkening hair color or applying dark pigment refers to processes that aim to add color rather than remove it. Enhancing natural pigments typically involves highlighting or adding shine to the existing color without significant alteration to the color depth. Therefore, the correct description of hair lightening accurately reflects the chemical process that changes the hair's visual appearance by reducing pigment rather than adding to it.