Permanent tattoos have long ceased to be solely a marker of a rebellious past or a hobby. Today, they are part of everyday aesthetics, a means of self-expression, and even a form of personal diary. But classic tattoos have one vulnerability – they don’t offer an “undo” option. Laser removal, as tattoo artists themselves note, is often more painful than the tattooing procedure itself. It is this pain and irreversibility that engineers from the University of Colorado Boulder are trying to mitigate with their development of inks that change visibility depending on lighting. The team’s work, described in the journal Matter & Light, became known on October 19, 2026.