Since she got in on the adult coloring book craze two years ago, Cheri Brown has spent more than $400 on 50 books holding intricate sketches that she embellishes with Sharpies, colored pencils and gel pens.
But in November, Brown shifted spending to digital products. She paid $100 for mobile apps including Recolor and Colorfy, which Comscore researchers say together reached 2.3 million users in the U.S. in March, less than 10 months after launching.
Brown, who crisscrossed the world as a diver for 30 years, now relaxes at home in the Los Angeles area. Eight hours a day, usually settled in an armchair or curled in bed, she pecks with her right index finger at an iPad Mini, lighting its screen with the blues, greens and silvers of the sea.
Brown, 63, even plans to pay upward of $700 for a stylus and an iPad Pro. It stores more artwork, boasts a bigger screen and offers greater precision.
"If I had $100 to spend on coloring, I'd be more likely to buy into a really good app than buy coloring books," she said. "You see where my purchases are starting to go."
The brisk rise of coloring apps threatens the enormous growth of coloring book publishers, who sold 12 million adult and children's coloring books in the U.S. last year - 1,100 percent more than in 2014, according to tracking firm Nielsen.
Coloring book enthusiasts insist they'd never abandon the pad and paper. But the concern is that, like Brown, people will become accustomed to the on-demand, dynamic enchantment of apps and ditch the old medium. That's what has happened as other throwback trends enjoy revivals - for instance how young adults subscribe to Netflix, not cable, to watch Nickelodeon shows from their past.
The issue reflects a spreading realization: It's dangerous for companies entrenched in making physical products or selling goods at bricks-and-mortar shops to not fight for online spending - and vice versa.
That explains why popular publisher Blue Star Coloring has found a partner to develop a coloring app, why movie studios are hawking apps filled with games and extra content, why rumors suggest online retail giant Amazon.com plans to open hundreds of bookstores and why many online shopping startups now rent mall space.
The colorist community is falling in line.
"There is a place for physical books," said Ilkka Teppo, 40, chief executive and founder of Sumoing, the Helsinki, Finland, startup behind Recolor. "You can much more easily try color combinations and styles on digital, then when you have more time, you can have the experience on print."
Business strategists agree books and apps can coexist. But it's not certain that every industry searching for physical-digital harmonies can escape the infamous decline that Napster, iTunes and Spotify unleashed on music companies.
"They can have a happy medium," said Elizabeth Spaulding, leader of management consulting firm Bain & Co.'s digital practice. But "simply waiting for it to play out is not a good answer. Figuring out trends that could displace their business is what matters."
With coloring books, Brown's move to digital offers one prediction of the future.
A friend's Facebook post about coloring apps and the tediousness of books inspired her digital transition. Brown carried a big tote with pencils and books when taking her infirm mother to long doctor's visits. Now, she slips the iPad into her purse.
Coloring a page takes days. So she's colored only 150 pages versus 300 digital creations in one-third the time. On screen, she colors three insect sketches during a doctor's appointment, mainly because elements like shading are instantaneous.
"With a touch of a finger, you've got it perfectly done - polished and smooth," she said.
After trying 20 of the 450 coloring apps, she settled on Recolor, paying a $40 annual subscription. It's best, she says, because you can erase by touch, quickly access recently used colors and color virtual 3-D objects. She expects Recolor to add better effects, which can make a drawing look like it's on canvas or other materials.
Pens and crayons cost hundreds of dollars. She spends less these days, occasionally splurging on 99-cent add-ons from third-party apps like Lumiere that animate Recolor drawings: Say putting shooting stars on an evening landscape.
Brown hasn't ditched books; she recently bought five because she wants to finish her coloring supplies. But she'll use her iPad camera to scan most pages into Recolor for digital alteration instead.
Showcasing her best digital work is possible too. She ordered a 2-foot-by-2-foot print from Costco of her coloring of Notre Dame Cathedral in Paris.
"Almost looks like a photograph," she said.
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Debra Matsumoto, a spokeswoman for Laurence King Publishing, which has sold 16 million art-book copies since 2013, acknowledged that heightened competition hurts sales. But the firm anticipates an enduring, sizable audience that "purposely seeks a very non-digital experience," Matsumoto said.
Count among them Shelly Durham, who runs the website Adult Coloring Book Reviews.
"Using a coloring app and saying you created art is like putting a TV dinner in the microwave and saying you cooked," she said. "They will never be the same."
Laurence King is out to prove it. One new book has gum binding for easy tearing and framing of pages. Another is a flipbook-style story, and a third has an accordion-like layout that unwinds 15 feet.
Apps maintain separate tactics to outlast - and buoy - books. Recolor is talking to publishers, advertisers and entertainment giants about constantly introducing the latest hot characters and themes into its app since digital rollouts can be fast.
"There will be major synergistic deals cut between intellectual property holders, booksellers and app vendors over the next 12 months," Teppo said.
Recolor recently raised an undisclosed amount for the nonprofit World Wildlife Fund by selling a pack of 10 animal drawings for $2.99. It also promoted the band Wolfmother by offering free album cover art for coloring.
Teppo declined to reveal overall sales figures, but data suggest a surging business. In April, Recolor added more than 2 million users and hosted 30 million coloring sessions - both double from March. About 3 percent of users subscribe, generating 5 cents in revenue per daily user, comparable to casual mobile games. Colorfy, the largest player in coloring apps, has five times as many users, according to estimates from tracking firm Sensor Tower.
Commissioning an illustration runs about $80 on average. Two launch every day, though striking partnerships could accelerate the pace 10-fold.
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Teppo's six-man team pursued Recolor almost a year ago after realizing three had wives hooked on coloring books. Smartphones, where tapping to insert a swatch of color could replace scribbling between lines, promised to make the art form easier. They launched in August.
About 80 percent of users are women or their children. Women tend to love puzzle games like "Candy Crush," but coloring provides the satisfaction of creation, Teppo said.
Others describe coloring as a way to relieve stress. That's partially the case with Brown. But entertainment is key, because she lacks options as a homebound caregiver.
She's forged friendships with app-colorists from Japan to Poland she discovered on the popular image-sharing app Instagram. But Brown avoids the "condescending" book-only colorists, she says.
"You'll always have artists that think the only way to be an artist is to pull out their coloring set," she said. "My heart is in the digital end of things."
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