Final answer:
The answer to the question is semi-permanent hair color, which partially penetrates and stains the hair shaft, fading over time with each wash.
Step-by-step explanation:
The type of hair color product that partially penetrates the hair shaft, stains the cuticle layer, and slowly fades with each shampoo is known as semi-permanent hair color. Semi-permanent color washes out over time, typically in four to six weeks, allowing for a gradual fade and less noticeable root regrowth. Unlike permanent hair color, semi-permanent dye doesn't chemically alter the hair's structure and is therefore unable to lighten the hair—an action that requires chemical lighteners like bleach. The final shade achieved with semi-permanent color is also influenced by the hair's original color and porosity, creating a more natural look with subtle variations in tone across the head, though it may not cover gray and white hair uniformly.