The discovery of the treatment in the methylene blue dye is quite fascinating. How exactly did someone figure that out for such a rare condition? And imagine being deep blue all your life and everyone knowing you as blue, then you take this blue pill and bam, you're pink as can be. Must have seemed like practical magic.
Makes you pee blue, can treat effects of carbon monoxide poisoning, etc. There were lots of opportunities for someone with blue skin to have encountered the stuff.