Final answer:
To achieve the most uniform hair color when performing a tint back to a darker shade, permanent hair color is the most effective option because it provides a deep and lasting color, compared to semi-permanent, demi-permanent, or temporary options, which tend to wash out and may not cover grey hair as uniformly. so, option 1 is the correct answer.
Step-by-step explanation:
When it comes to returning hair to a darker color, also known as a tint back, the most uniform color is typically achieved using permanent hair color. Permanent coloring requires a three-step chemical process including an oxidant and compounds such as 1,4-diaminobenzene or 2,5-diaminotoluene, resulting in a chemical change to the hair's structure. This alteration allows the color to penetrate deeply and cover grey hair more uniformly compared to other types of hair colors.
In contrast, semi-permanent hair color washes out after four to six weeks and cannot lighten hair, nor fully cover grey hair uniformly. Demi-permanent hair color may also have some difficulty in covering grey hair entirely. Finally, temporary hair color simply coats the surface of the hair and washes out after one or two shampoos, so it would not be effective for a tint back process intended for longer-lasting results.