Final answer:
For 70–80% grey hair tinting back to its original color, it is advisable to select a hair dye that is one shade lighter than the original color for a more natural result. The correct option is A.
Step-by-step explanation:
When a client's hair is 70–80% grey and they wish to tint it back to its original color, it is generally recommended to choose a shade that is one shade lighter than the original. This approach can lead to a more natural look since grey or white hair can appear slightly lighter than hair that still holds its natural pigment. Furthermore, as the grey hair may have different porosity, it won’t absorb the dye the same way as the non-grey hair, potentially resulting in a harsher look if a darker shade is used.
Therefore, option (a), one shade lighter than the original, is often the best recommendation. To tint a client's hair that is 70–80% grey back to its original color, you should choose one shade darker than the original color. This is because grey hair is usually lighter than the natural color, and choosing a darker shade can help achieve a more natural result. If the client's hair is already a dark color, going one shade lighter (option a) may not provide enough coverage for the grey.