What tool is most commonly used when applying hair dye?

The bowl and brush set is typically the most commonly used tool when applying hair dye. This combination allows for precise application of the dye to the hair. The bowl is used to hold the dye mixture, while the brush is specifically designed to aid in evenly distributing the dye through the hair strands. This method ensures that the color is applied uniformly and helps avoid staining the skin or surrounding areas, which can happen with other tools.

In contrast, the other choices do not serve the same purpose. A comb and scissors are essential for cutting and styling hair, while a hairdryer and diffuser are used for drying hair after washing or styling, rather than applying color. Rollers and clips are typically used to set or style hair, not to apply dye. Thus, the bowl and brush set is specifically tailored for the task of applying hair dye, making it the correct choice.