To ensure that you never have roots it is necessary to cover your natural color as your hair grows. This is required after three weeks to ensure best results. Application of regrowth color to give an overall even result, ensuring that your roots match the rest of your hair.
This ensures maximum condition of your hair This has to be done very precisely as not to overlap color, which can cause banding with an overlay of color causing the middle of your hair to be darker than the roots and the ends. This will affect the overall color of your hair and the condition of your hair. If this happens it is very difficult to remove from the hair without using a color reductor to remove the banding. In short this is not something that you can do yourself and expect good results from.
It must be done by a certified colorist to ensure that your hair looks great and you have fabulous even hair color from root to tip.