The year 2015 would perhaps be best regarded as the year adults got back to coloring, and the popularity of adult coloring books has yet to die down as the New Year ushered in. Plenty of upcoming titles are slated to be released this year, and they are predicted to also become bestsellers.

China's bestselling book for 2015 was "Secret Garden," the adult coloring book released by Johanna Basford, according to Mashable.  Three of the Top 10 bestselling books for 2015 were "Secret Garden," "Enchanted Forest" and "Adult Coloring Book: Stress Relieving Patterns," and a roundup of upcoming adult coloring books - until April 2016 - was listed for the first time by Publishers Weekly. 

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Many artists are cashing in on the trend as it has become big business, and even online entrepreneurs are going into self-publishing or mass production. "To have a commercial success, you need hundreds and hundreds and hopefully thousands and tens of thousands," said business specialist Hillary Tattersall, according to Voice of America. She has been working with an e-commerce operator to expand her business on the Internet.

"I had the idea, and then I discovered that, while adult coloring books had been around for a while, they're just now having some sort of crazy, explosive acceptance. That motivated me to follow through," said artist Staci Dickerson, Post Independent reported.

"I had all these drawings and about a month ago my wife said 'You know, these adult coloring books are kind of all the rage. Why don't you create one?' I thought, why not," said Kip Hubbard, another artist.

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Neuroscientists claim that working on adult coloring books, as opposed to drawing or making one's own art, helps with "decision fatigue," New York Magazine noted.  It's a similar point Basford raised during an interview. "Chances are last time you picked up pens and pencils, you didn't have a mortgage or, like, a really horrible boss or anything. It's just a really nice way to be creative," said Basford, according to NPR. "You don't have to sit down with a blank sheet of paper or, you know, have that scary moment of thinking, what can I draw? The outlines are already there for you."

Neuroscientists also explain that some people get into the hobby for the sake of enjoyment and not exactly creativity. "As we get older, we lose our playful side," psychologist Scott Barry Kaufman said. "I think anything that resembles our childhood play can get us back into that frame of mind as an adult."