Root hair is the new hair growth; it’s un-colored and reacts differently to color than the lengths of the hair. The length of your roots depends on how long it’s been since your last color. If it has only been a few weeks since your last color, your roots may only be a half inch to an inch long. If it has been several months, roots can be up to 2 inches long. The rest of the hair is considered the lengths, or the ends. If you’ve never colored your hair before, or if it’s been longer than 6 months, you will treat your roots and lengths the same way.