What tool is commonly used for applying hair color?

The tool commonly used for applying hair color is the applicator brush. This specialized brush is designed to help distribute hair color evenly and accurately onto the hair, ensuring thorough coverage from roots to ends. The applicator brush typically features a tapered design, allowing for precision in application, especially in areas that require careful detailing, such as the hairline or partings.

The other options do not serve this purpose effectively. A hairdryer is primarily used for drying hair or setting styles but does not aid in the application of color. A comb is useful for sectioning and detangling hair but is not designed to apply color itself. Scissors are tools for cutting hair, which is unrelated to the process of applying hair color. Thus, the applicator brush is the optimal choice for this task.