Though I vaguely recall scribbling in the lines of Lion King and A Bug’s Life illustrations in elementary school, it was not until high school that I returned to coloring. I took a class on neuroscience for which one of the required texts was a book called The Human Brain Coloring Book. It’s a massive tome, and I still have it — I’ll probably never get through its hundreds of pages. It would not be an overstatement to say that what I remember of synaptic transmission and Wernicke’s area is entirely indebted to hours spent filling in the brain’s anatomy in emerald, cornflower, crimson, and marigold. Later, I purchased a Hello Kitty activity book in the dollar aisle at a Target in Warwick, Rhode Island just before I moved into my first apartment. An impulse buy, I got some crayons to go with it, one of those Crayola 24-color boxes. I kept it in my top desk drawer and occasionally pulled it out when I needed a break from writing my senior thesis.

It takes what little artistic ability I possess to color an illustration. Perfectionist that I am, I lean down, head nearly touching the page, mastering a particular uniform shade or the transition between two colors. Ask me to draw anything from scratch, though, and that’s where my talent falls short. When I began coloring again after my teenage hiatus, perhaps it was in order to feel a sense of artistic accomplishment without the inevitable disappointment of a failed line drawing.

Coloring is its own kind of creating. Recently, coloring books have gotten a lot of play among adults for their purported anxiety-reducing qualities. But there’s something more at stake for artists who attach their names, their style, and their portfolio to a book meant for public interaction and completion. Coloring implies a sort of collaboration with the artist who put the book out there. I might work my way through Hello Kitty, playing tic-tac-toe with myself and adding color to her friends and family, but it doesn’t yield quite the same creative reward as contributing to the works-in-progress of, for example, Steve McDonald or Millie Marotta, two artists who moonlight as coloring book authors.

Marotta’s first book, Animal Kingdom, was released about four months before the “coloring book boom,” as she described it, really launched. But she — like many artists who have come to profit from the renewed interest in coloring — has been creating for far longer and for far more varied outlets than her publisher alone.

“I was painting, I was using just brushes and black India ink, I was embroidering onto paper, I was sewing on the sewing machine onto paper, I was using collage, I was doing black fine line drawing,” she recalled. “This very stylized, full of pattern, very fine black and white artwork have become predominant.” Her portfolio had already begun to lend itself to the coloring book form when a publisher approached her about compiling a book.

McDonald, whose book Fantastic Cities debuted this month, found his style similarly stripped down over the course of his career. He didn’t begin making coloring books until he and his family relocated to Indonesia — he had carved out a place for himself in the North American gallery community, but was unmoored by the move. “It was either hit the streets in Indonesia and start approaching the galleries there, hopefully, or ship work back to North America, or find a new medium,” he recalled. “And the new medium is coloring books.”

While these artists’ styles gradually arced toward the kind of illustration one might expect in a coloring book — albeit an elaborate one — Souris Hong’s Outside the Lines accomplishes the reverse. Though some graffiti artists, comic artists, and graphic artists — whose work might be expected to suit a coloring book — appear in Outside the Lines, so too do photographers and musicians. Hong curated a compendium of nearly 150 contemporary artists, some of whom submitted works from their back catalogue adapted for coloring. Others composed entirely new art, resulting in a survey of the contemporary art landscape that runs the gamut from monochromatic, geometric patterns to photographs rendered as line drawings.

Hong’s daughter, owner of an enviable library of coloring books from around the world, had gravitated towards adaptations of pieces by established artists. Her mother then thought, “Wouldn’t it be cool if she could color in her dad’s artwork, or our friends’ work?”

This collaboration is not native to coloring, but it has rarely had such a mainstream audience. When I was a teenager, I participated in a photography project where one photographer shoots a roll of film, winds it back up, and mails it across the country. The recipient then shoots over the same roll, double-exposing the images and creating serendipitous, often incongruous, fused images of landscapes and individuals. The concept is the same, though the output may be different — art as a  collaborative work in progress.

The coloring books represent a dual function of portfolio and collaborative art. “I love the idea that I’ll be involving 10-year-olds and middle-income retirees in the process,” McDonald said — and these are just two groups who might not normally happen upon one of his gallery exhibitions. But even before the recent “massive tidal wave of adult coloring book interest,” as McDonald described it, artists consistently turned to the medium to publicize their art. Keith Haring and Andy Warhol both published coloring books.

With coloring books, entirely new audiences can interact with artwork in a multi-dimensional way that isn’t necessarily possible when viewing a piece of art on a gallery wall. The aloof atmosphere of a gallery or museum acts as a method of control; the curated exhibition space also curates interactions with the art, because of social codes surrounding how one behaves in the space and around the art. Quiet reverence is expected; disruption is frowned upon. Coloring books allow adults and children alike to interact with visual art in a far more permissive environment, sometimes democratizing the art-making process.

For example, when Outside the Lines launched, Hong recalled, over 50 of the artists included gathered at LA’s Museum of Contemporary Art in support. For the children who showed up, “it was a day of yes,” Hong said. “Instead of being told no, don’t touch that, or no, no running, or no, come over here, it was like, yes, you can color on the walls.” Coloring books can make a museum more accessible to the masses: Barnes & Noble as the new Christie’s; Target as the new Sotheby’s.

The coloring book assumes that visual art is open-ended and incomplete. The raw material — the blank book — is the same across all individuals, but the output will never be the same. This can be a daunting prospect for the artists, losing dominion over what they put out into the world. Marotta recalled her trepidation prior to the release of her first book — uncertainty about how the public would respond to a collection of her work, or what they might do to it. Add in the popular conceptions of coloring books (“I always considered it sort of a lowbrow form of art,” McDonald said), and it might not appear the best medium for a serious artist.

But coloring books can also allow audiences to interrogate what, exactly, defines “a serious artist.” Who hasn’t been to a gallery and thought (only on occasion and with a mixture of shame and excitement), I could do that? Coloring books synthesize so many binaries of the traditional art-making and -displaying process: They bring artist and consumer closer, help collapse the distinction between viewing and creating, and complicate the distinctions between “serious artist” and “amateur colorer.” The book is like a tiny microcosm of a gallery. You can hold it in your hand, and it contains art that you might not be able to create from scratch, but that nevertheless is both yours and the artist’s.

Theo Nicole Lorenz, the author of coloring books including Fat Ladies in Spaaaaace and Dinosaurs with Jobs, described their own interaction with Johanna Basford’s book Secret Garden: “I cannot for the life of me make designs that intricate,” they said. Like Marotta, Basford’s work has appeared on commercial packaging and book covers, but her coloring books have been a massive success and even spawned online tutorials on how best to color in her illustrations. Lorenz said they spend up to a week filling in one of Basford’s line drawings. By the end, they look back on their accomplishment and think, “I kind of want to hang it on my wall.” (Hong’s most recent effort, Outside the Lines, Too, has perforated pages to allow colorers to tear out their completed works.)

By involving their audiences in the art-making process, the artists can create work designed for their particular readers. Lorenz said they often post their concepts to Twitter to gauge readers’ reactions before developing a book. The concept for Lorenz’s first book, Fat Ladies in Spaaaaace, was the direct result of peer pressure — “Where are all the fat butches in space?” they were asked during a panel about fat acceptance. They immediately illustrated the idea, and a friend and co-panelist urged them to do more. “I started throwing out concepts and saw what stuck,” Lorenz explained. For them it’s an extension of, rather than a departure from, more conventional methods of storytelling (Lorenz is a comic illustrator with a degree in creative writing, so they’re a storyteller first and foremost).

“Coloring books offer a way to be creative without that daunting blank page in front of them,” Marotta said. “It gives them a starting point and something to work with.”

Artists who create coloring books leverage the medium in order to bring their art to audiences and their audiences to art. Audiences post their responses to new concepts and new illustrations via social media, invoking a unity across space, ages, genders, and interests. It’s reciprocal at every stage.

As McDonald noted, coloring books are just another medium, yet somehow they’re not “just another,” because they promote access rather than reserve. I still haven’t finished the Hello Kitty book, or the Bun B Coloring and Activity Book, or the Human Brain Coloring Book, or the Geography Coloring Book, or the one simply entitled Feathers that I found in a tiny bookstore one summer. I’m terrible at finishing anything — endings have never been my strong suit — so to me it seems like an added bonus that these coloring book artists get to intentionally leave their illustrations open-ended. They create collaborative-minded art that leaves their hands unfinished, and my collection, too, will always be a work in progress.