Depends on how you do it, really. Most of the candy color dyes these days are semi-permanent or temporary colors, so they don’t have the same harsh chemicals that permanent dye used to have. The most dangerous chemical in the process is the peroxide bleach, and you can get really gentle formulations of that now for bleaching your mustache.
That sounds like it could go horribly wrong if you don’t know how to use the chemicals.
Depends on how you do it, really. Most of the candy color dyes these days are semi-permanent or temporary colors, so they don’t have the same harsh chemicals that permanent dye used to have. The most dangerous chemical in the process is the peroxide bleach, and you can get really gentle formulations of that now for bleaching your mustache.