Tokyo Ghoul is a widely popular and successful anime,even though there’s quite a lot of difference between Manga and anime. It’s an anime that tells the journey of Kaneki, a boy who made the wrong choice by going on a date, which ultimately led to chaotic affair such as questionable surgery, human centipedes and crazy masks!
In the final episode of season 1, we can see Kaneki getting brutally tortured. After a certain point of time, he embraces himself of being a ghoul rather than a human, that moment his nails turn black and his turns white instantly. This is an actual medical condition called Marie Antoniette syndrome.
This is caused by extreme amount of stress and psychological trauma as we see Kaneki being put through. This condition was named after Queen Marie Antoninette when she and her family were trying to flee Paris for high treason. On the night of her execution, her hair had turned fully white all of a sudden.