L’Oreal recommends waiting two weeks
Most permanently colored hair grows at a rate that will require touching up the roots at least once every six weeks. The L’Oreal website recommends waiting at least two weeks between hair color applications. The recommendation is to wash hair, wait at least 24 hours and then apply the hair color.
Permanent color lasts longer than semi-permanent
Permanent hair color does not wash out like semi-permanent color does. Semi-permanent color washes out in as little as 10 shampoos, while permanent hair color lasts until it grows out or is covered up with another hair color. Permanent hair color needs to be reapplied as the hair roots grow out, usually every four to six weeks.
Although you can recolor your hair every two weeks with L’Oreal hair color it probably wouldn’t be very practical to do so because of the time and expense involved. Unless you are opting to change your color entirely, touching up the roots every four to six weeks is much more economical than coloring your hair every two weeks.