They call themselves lemmings. And like those mythic rodents, whose herd mentality is said to be so strong as to lead them off cliffs, these women are united in a mission that, to outsiders, may seem baffling and even berserk.

The objects of their desire — what they track on eBay, rhapsodize about on their blogs and search for in faraway lands — are bottles of old nail polish. More specifically, discontinued varieties that come in colors no longer available but that are still out there, sitting forgotten on the shelves of manicurists and out-of-the-way stores, just waiting to be found by some lucky lemming who will add them to her collection, cherish them and post them on Instagram for other members of this unlikely subculture.

One white whale for those in the know is Starry Starry Night by Essie, often abbreviated SSN. The navy blue pigment, spangled with silver glitter, is beloved for its “buildability,” meaning that in just a few coats one can achieve an alluring depth.

For those who can’t afford a bottle of Starry Starry Night (an eBay auction for one ended at $250 last month), pendants, earrings and other small pieces of jewelry painted with the color are sold online.