It’s a craze that’s sweeping the whole world: adult coloring books, which often become the top-selling books on Amazon. According to Nielsen Bookscan some 12 million coloring books were sold in 2015 - 12 times the number sold the year before.

Pictured: From “The Official Game of Throne Coloring Book” (Bantam).

By CBSNews.com senior producer David Morgan

Lacy Mucklow, a licensed clinical professional art therapist who writes about the field of art therapy, worked with British artist Angela Porter on the bestselling “Color Me Calm” (Race Point). The designs in this and their other books offer geometric patterns, mandala designs, and bucolic scenes that draw upon Jungian archetypes.

“I think the act of coloring in itself is generally calming and relaxing for people,” Lacy Mucklow told CBS News’ Rita Braver. “But the content can really help. Images evoke different memories, different feelings in people.  So for instance, we had some wooded scenes, nice mountain cabins that people think about relaxing and going on vacation about.  Or being by water - people usually enjoy beaches or enjoy being by the lake.  And so a lot of these images bring up particular memories that people have.”

A Washington, D.C. library coloring group meets. 

Mucklow suggests there are stress-relieving benefits for colorists: “They have stressful parenting days. They had medical issues and they colored while they were in hospital, or color in recovery. I’ve heard about several people who have PTSD and they find that it helps them calm down.”

From Scottish illustrator Johanna Basford’s “Secret Garden” (Laurence King Publishing), a book filled with elegant and fanciful images that is credited with spawning a coloring book trend.

Tools of the trade.

Rita Braver asked Lacy Mucklow, “Can people really color their way to happiness?”

“I think it can help,” Mucklow replied. “It’s individualized. I can’t make somebody feel anything in particular.  But the purpose behind the images is to help gear people in that direction.”

“Serious meditation is its own art form, and it takes a lot of discipline to do,” Lacy Mucklow told CBS News. “But this is something that is similar to that and it can get you in a state that produces similar types of results.  I wouldn’t call it meditation per se, but it has a meditative quality.”

A finished masterpiece.

From Rony Takos (Okat) and Hugo Seijas’ “Doodlers Anonymous Epic Coloring Book” (M Studio).

The website Doodlers Anonymous is an online Mecca for colorists.

A city design by C.J. Loo, from “Doodlers Anonymous Epic Coloring Book.”

From Aye Jay’s “Graffiti Art Coloring Book” (Chronicle).

Steve McDonald’s art career started in what he calls “a very traditional way - I went to art school in Canada and I started painting landscapes with oils.”

His architectural and aerial illustrations became more and more complicated but, he told Rita Braver, “I always loved the drawing far more than I loved the painting of it.  I consider myself good with color but for years, I wished I could say, ‘This is finished.’ The great thing about the coloring book is I’ve been able to create this whole range of drawings which I have absolutely adored creating, but I was able to stop at that point and let everyone else color them!”

McDonald’s coloring books (about places “real and imagined”) include “Fantastic Cities” and “Fantastic Structures” (Chronicle Books), which are now sold in approximately 30 countries.

“I work pretty closely from photographs,” Steve McDonald said. “I want you to be able to look at that scene of Paris and find your own window, or if you’re from San Francisco and your house is in that drawing, I want you to be able to find your house, and I want it to be accurate.

“I’ve seen people attack ‘em with watercolors and they’re ignoring the lines completely. They’re putting different tones everywhere. I’ve seen people attack them with markers and the lines are there as a guide. The book is there as a guide. This is just to give you something that you can take forward and be creative with.”

From Steve McDonald’s “Fantastic Structures.”

McDonald is not ready to jump onto the therapeutic claims made for coloring books. “I’m not gonna be so bold as to claim that my book will make you a mentally healthier person,” he said. “In fact, there [are] people that say some of the drawings in that book will make you less mentally healthy! But the point is, it’s a book that is gonna help you be creative, and creativity is always good.”

North Korean dictator Kim Jong Un plays Battleship with Donald Trump in M.G. Anthony’s “The Trump Coloring Book” (Post Hill Press).

For more info:

Delineation: The artwork of Steve McDonald (Official site)

“Fantastic Cities: A Coloring Book of Amazing PlacesReal and Imagined” by Steve McDonald (Chronicle Books)

Adventures in Art Therapy (Lacy Mucklow’s official site)

“Color Me Fearless: Nearly 100 Coloring Templates toBoost Strength and Courage” by Lacy Mucklow; Illustrations by Angela Porter (Race Point Publishing)

Adult Coloring Club, Northeast Neighborhood Library, Washington, D.C.

“Doodlers Anonymous Epic Coloring Book” (doodlersanonymous.com)

Adult Coloring products from Crayola