OK, this is really rad.
Some students at a British high-school wanted to wear colored nail polish, but their school prohibited any kind of make up. They found the ban to be unfair so they came up with a novel approach that would keep them out of detention, but allow them to wear their blood-red fingertips.
They invented nail polish that disappears when its not in the sun.
Much like G.I. Joe’s Zartan, the polish is bright red in the sunlight, but fades to an almost invisible state indoors.
This wasn’t some big cosmetics company that came up with this idea and perfected the implementation, it was school-age girls in the UK.
I love this kind of stuff.