Which tool is commonly used to apply color to hair?

The applicator bottle is the preferred tool for applying color to hair due to its design, which allows for precision and control during application. This tool typically features a pointed tip or nozzle that enables the stylist to apply color directly to the roots or specific sections of the hair with minimal mess. The bottle can also hold a sufficient amount of color, making it convenient for larger applications, whether for full head color or touch-ups on specific areas.

In contrast, a hairbrush is typically used for distributing color evenly after it has been applied but is not the primary tool for application itself. A round comb is useful for sectioning and styling hair, but it is not designed for applying color. A flat iron is primarily used for straightening or curling hair and has no role in the color application process. Understanding the function of these tools is crucial for effective hair coloring.