Making Disposable Contact Lenses Opaque?

I’m looking for a method to make my disposable contact lenses opaque once I finish using them. Since they are going into the trash regardless, it seems like they could serve well as blindfolds in different scenarios. My research online mostly brings up retailers selling decorative lenses that remain see-through despite being opaque-looking. Also, I’ve heard that food coloring tends to irritate the eyes and merely tints the lens rather than blocking sight entirely. If anyone has other ideas, please share.