Which technique is performed on the surface of the hair to create a highlighted or lowlighted colour effect?

The technique that is performed on the surface of the hair to create a highlighted or lowlighted colour effect is balayage. This method involves hand-painting highlights onto the hair in a sweeping motion, which allows for a more natural, sun-kissed look. It focuses on the surface of the hair, creating dimension and contrast while maintaining depth in the base color. Balayage is particularly favored for its soft, blended result, which can be tailored to suit individual styles and preferences.

Although freeform may seem like a possible choice, specifically, balayage is the method most closely associated with the technique of painting on the hair's surface to achieve that highlighted or lowlighted effect. Other techniques mentioned, such as double-process and base to ends, do not focus solely on surface application in the same way that balayage does.