Final answer:
For a lighter color result during a retouch in cosmetology, the mixture should be applied to the new growth area to avoid over-processing. A color remover or lightener may be needed, and product instructions and strand testing are recommended.
Step-by-step explanation:
The question pertains to the process of color retouching in cosmetology, specifically when wanting to achieve a lighter color result on previously dyed hair. For a lighter result during a retouch, the mixture should typically be applied to the new growth only. The new growth is the area of hair that hasn't been previously dyed. To avoid over-processing and potential damage, the mixture should be applied carefully, ensuring not to overlap excessively on previously lightened or dyed areas. In some cases, a color remover or lightener may be used, depending on the desired lightness and the current state of the hair. Always follow the specific product instructions, and consider performing a strand test before applying the product to the entire head.