Where should color be applied for a retouch service?

For a retouch service, color should be applied up to the line of demarcation. This line indicates where the previously colored hair meets the new growth (the regrowth). Applying color to this area ensures that the roots and the previously colored hair blend seamlessly, resulting in a uniform color throughout.

Focusing on this specific application technique minimizes the risk of damage to the lengths and ends of the hair, which may already be colored and potentially more porous. Additionally, applying color solely at the line of demarcation helps refresh the hair's appearance without over-processing the previously colored hair, maintaining its health and vibrancy. This approach is essential in color correction and maintaining the overall aesthetic of the hairstyle.