Final answer:
A deposit only color adds semi-permanent pigment to the hair's surface without altering natural pigmentation, leading to natural-looking color variations and less noticeable regrowth.
Step-by-step explanation:
The action of a deposit only color on the hair, typically achieved using a semi-permanent hair dye and an appropriate developer, is to coat the outer layer of the hair with color without altering its natural pigmentation. Unlike permanent hair coloring, which requires an oxidant to penetrate the hair shaft and react with molecules inside the hair to create a permanent color change, deposit only color adds pigmentation only on the external surface of the hair. This process is gentler on the hair and washes out over a period of typically four to six weeks. As a result, root regrowth is less noticeable, and the final color of each strand will vary depending on its original color and porosity, leading to a more natural look.
However, it is important to note that since the color is deposited without lifting the hair's natural pigment, gray and white hair may not absorb the color uniformly. While a few gray and white hairs can blend sufficiently, over time, a purely semi-permanent color might not sufficiently mask the increase in gray hair, prompting a move to permanent coloring options combined with semi-permanent base color and highlights.