Hair colors of condemned Prisoners have been reported in history to have turned gray overnight before their executions. Cases in point are Thomas More in 1535 and Marie Antoniette in 1793.
According to historical reports, condemned prisoners have been known to suddenly turn gray overnight before their executions. Cases in point are Thomas More in 1535 and Marie Antoniette in 1793. However, there have not been any modern reports to corroborate these assertions of hair color turning gray over night, except for cases of chemotherapy and/or effects of hormones on pregnant mothers.
Fear and Extra-ordinary emotions
Fear and extra-ordinary emotions can indeed change haircolor although not instantly because your psychological state has a significant impact on the hormones that can effect the amount of melanin deposited in each strand of hair, but the effect of emotion takes a long time to be seen. The hair you see on your head emerged from its follicle a long time ago. So, graying or any other color change is a gradual process, occurring over the course of several weeks, months, or years.
Diffuse Alopecia Areata
Your emotions can’t instantly change the color of your hair, but it is possible one could turn gray overnight under certain medical conditions such as Diffuse Alopecia Areata which also causes sudden hair loss. The biochemistry of alopecia isn’t well understood, but in people who have a mix of dark and gray or white hair, the white hair is less likely to fall out such that when the rest of the colored hair fall out as a result of the effects of alopecia, the person suddenly appears to have developed white or gray hair overnight.