Final answer:
Dyes are the small compounds that can diffuse into the hair shaft and are contained in the tint formula. They differ from pigments that are used in paint. Dyes are used in permanent hair coloring along with oxidants and coupling agents.
Step-by-step explanation:
The small compounds that can diffuse into the hair shaft and are contained in the tint formula are dyes. Dyes are colorants that dissolve in the hair shaft. They are different from pigments, which are granular solids incorporated into paint to contribute color. Dyes are used in permanent hair coloring along with other components such as oxidants and coupling agents.