University of Colorado nanoengineers develop Magic Ink - tattoo ink that reacts to UV light changing it's visibility. They are working under a grant from the NSF to discover medical applications for reactive / color changing tattoo ink.

"The name Bang Bang might not ring a bell, but the tattoos he’s done are very public: They’re cascading down Rihanna, scattered across Miley Cyrus, and peering out from LeBron James, among others. Turns out, Bang Bang loves tech."

https://coloradosun.com/2023/08/29/smart-ink-tattoo-university-of-colorado/