Multicolored hair where the color of the hair closest to the scalp (ie the roots) is a different color from the rest of the hair. This is typically visible where the hair parts on the head. This color difference may be unintentional such as with dark roots and hot roots, or it can be intentional such as with shadow roots.
Dark roots or over-grown roots occurs when dyed hair (frequently blonde) has not been maintained and the person's natural darker hair color has returned with their new hair growth. Hot roots is an error during the hair dying process which results in the hair closest to the scalp to be a different color than the rest of the hair, commonly the hair color closest to the scalp is lighter and/or more vibrant than the rest of the hair. Shadow roots (also known as root shadow or root smudge) is similar to dark roots but is intentionally dying the hair closest to the scalp a color close to the person's original hair color so that it forms a color gradation as their natural hair color returns as their hair grows.