Get back to Blonde
A: Okay, since he has used a permanent hair color, he's going to have to lighten the hair to a semblance of the former color, use a color remover or simply let the color grow out.
If you opt to lighten the hair or remove the color yourself, I suggest that you use a color remover kit, such as Colorfix, since it is designed to fully remove the hair color without being as harsh as using a two-stage bleaching and coloring process.
Be aware that many users report that color removal products usually leave the hair an unnatural, flat, beige-looking color, and that your son may want to use a light blonde, deposit only color to add some "tone" to his hair color after removing the permanent color he added for his video.
If you think you'd rather go with lightening and re-coloring the hair, seek a professional salon for the service. (You should do the same for the color removal if you feel insecure about doing it yourself.) The salon professionals can better assist your son in lifting his hair color safely to a reasonable level.
Of course, some young men - particularly those who have shorter hair - simply opt to cut the hair off in this situation and grow it in fresh. If your son's hair is an inch long or less, he can have the hair back to its current style (with no color) in two months, give or take a week.
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See also:
Hair coloring
Men's hair and hairstyles
Temporary, semi-permanent and permanent hair color