Can I use Root Reboot if my hair is 100% white?

Yes. Root Reboot is designed to blend gray, rather than cover like permanent color, so Root Reboot will make your regrowth line much less obvious. Root Reboot helps camouflage that line and buy time between permanent color applications. For maximum color deposit on 100% gray or white hair, you can either leave the color on for an extra 5 minutes or choose a shade darker than your typical permanent color.