On warm nights, Bobby Francis and his three roommates like to hit the balcony of their Manhattan apartment, pull out their phones and change the color of the New York City skyline.
With a few taps, spires atop two Midtown skyscrapers flicker blue, red and orange.
“It doesn’t feel like something I should have access to at all,” said Mr. Francis, who turns 23 on Wednesday. The consultant sleeps in the former kitchen of a converted two-bedroom apartment.
Yet he does. Mr. Francis and his roommates are members of New York’s latest exclusive club: Spireworks, a much whispered-about free app that allows users to change the colors of the spires atop two of New York’s tallest buildings.
The only way to join is to be invited by a current user, so access has spread through an unlikely network of colleagues, friends and denizens of the city’s rooftop bars. Among fans, invites remain a precious commodity, creating a new class of haves and have-nots.
The have-nots plead their case on social media, and a black market for invitations has opened up on Craigslist.org and other websites, where they sell for $100 and up. The app owners recently asked Tinder, the dating app, to take down a profile hawking a Spireworks invite for $1,000.
Anthony Papavasiliou, a 38-year-old owner of a Fort Lee, N.J., Greek restaurant, has been posting on social-media sites seeking access since a friend showed him the app in action two years ago. He donated $250 to Creative Time, a New York nonprofit that supports artists that was giving out invites, but he didn’t nab one.
“I just have to have it,” he said, describing himself as “the kind of guy who wakes up at 3 a.m. to get the latest iPhone.”
The app lets users control the colors of spires atop two buildings: One Bryant Park, dubbed the Bank of America Tower after its main tenant, and 4 Times Square, home to law firm Skadden, Arps, Slate, Meagher & Flom LLP and distinguished by a large neon logo of fashion label H&M .
The app is the brainchild of Mark Domino, a digital-media artist who built “multisensory musical instruments” while a student at Brown University. He is the son-in-law of Douglas Durst, the real-estate tycoon whose family company, the Durst Organization, owns the two midtown office towers. Mr. Domino works as director of digital media at Durst.
After sunset each night, app users can log in, choose a building and select from a palette of colors during a two-minute session. Options for sparkles add pizazz. Cloud-hosted software sorts the requests and instructs the lights that line the two spires, a combined 716 feet tall.
Usually only five users are allowed to actively change the colors at a time. So, on busy nights, a digital queue forms. Waits approached half an hour on July 4th this year. Red, white and blue were the only colors available that night.
“What is more powerful than getting control of the city?” asked Vincent Bruneau, the 36-year-old CEO of a company that runs a corporate-meeting app who scored an invite. “It’s kind of supernatural.”
Last year on a trip to Paris, Mr. Bruneau received a 6 a.m. call from a friend back in New York begging him to change the color of the spires so he could impress guests at a party. Bleary-eyed, Mr. Bruneau obliged.
Durst has added One World Trade Center, which it manages, to the app on special occasions, including the U.S. Open tennis tournament, the NYC Marathon and World AIDS Day.
Seven years ago, Mr. Domino wrote the code to control the spire lights. At the Durst holiday party 2010, his father-in-law hit the button for the inaugural color change. Durst employees invited a few friends and tenants, who each got a few invites to give away.
The app’s community grew slowly and by word-of-mouth. In the past year, it has increased dramatically and the number of users is now approaching 10,000, Mr. Domino said. Each user can offer five invites.
Earlier this year one couple turned Durst’s Times Square spire blue to reveal the gender of the baby they were expecting, and a handful of men have used it in marriage proposals, Mr. Domino said. One user hid his phone in his pocket and bet tourists near Times Square that he could change the spire’s color as a magic trick, Mr. Domino said.
At a 2015 party celebrating the listing of a posh Tribeca penthouse with clear views to Midtown, a broker with the app wowed potential buyers as they played rooftop croquet while being serenaded by a string quartet. “Talk about being king of the castle,” said Elizabeth Kee of Core, the listing agent. The apartment sold for $8.3 million.
When Natalia Krasnodebska got a Spireworks invitation from her friend Ashley Zelinskie, she said she fired off a thank-you tweet. Almost immediately, Ms. Zelinskie, an artist currently showing at Sotheby’s , was flooded with dozens of requests for invitations from strangers. She said she declined them all.
Mr. Domino said he didn’t like the velvet-rope vibe that has grown around the app. He said he wanted Spireworks to be an “open system to share in moments of discovery and play.”
He said he is looking for ways to cut down on “bootlegging,” perhaps by doing away with the invitation system in favor of one unlocked by charitable donations. Durst said it has had preliminary discussions with charity partners but declined to name them.
Mr. Domino also said he was dismayed how many of the app’s most ardent fans are young men who want to use it to pick up women.
He said that in a recent survey of Spireworks users, bartenders at the Boom Boom Room, a millennial hot spot atop the Meatpacking District’s Standard Hotel, complained the club was saturated with men using the app to try to seduce women.
James Geraci, a recent college graduate from the Boston area, tweeted to the official Spireworks account during a Memorial Day visit to New York seeking an invite. Some women were coming by his hotel room, which faced the spires, and he said he thought the app would be “a power move of a pickup line.”
No one ever responded. Mr. Geraci said he “ended up having to try to impress the girls the old-fashioned way.”