Chemical services should not be performed on hair that has been coloured with any of the following products, except?

Chemical services, such as perms or relaxers, can lead to serious damage if applied to hair that has already been altered with certain types of coloring products. Weekly rinses are often less intense and temporary as they generally add color without changing the hair's structure significantly. These products typically wash out after a few shampoos and do not penetrate the hair shaft in the same way more permanent dyes do.

In contrast, hair dyes, permanent colors, and lightening products involve chemical processes that alter the hair at a structural level. This can result in weakened hair that is more susceptible to breakage and damage when subjected to additional chemical services. Therefore, performing chemical treatments on hair that has been treated with more permanent coloring products is often contraindicated.

By selecting weekly rinses as the exception, it acknowledges that these products do not compromise the integrity of the hair to the same degree as the other chemically intensive treatments do, allowing for further chemical services to be performed without the same risk of damage.