Hanna Karlzon is a Swedish illustrator who has published a bunch of adult coloring books. Ah, but not just any books. The art is amazing and the quality of the books is outstanding as they are hardcover books.
Now, the caveat is that they are double sided books and a lot of the picture designs go to the end of the spine, and numerous of the designs are two-page spreads. These factors made the books undesirable to me at first because I have problems with my arms that make it difficult to color in a book. I have to remove the pages first, so I usually only buy books that have perforated pages. I've also spiral-bound a few, but I am picky because a book has to be totally worth the extra expense of doing so.
For those reasons, I did not get one of the Hanna Karlzon books until recently when I won a copy of Summer Nights. I was ecstatic and could not stop flipping through the book. Alas, it still presented the challenges. So, don't tell anyone, but I actually had the binding cut at a Kinko's store. I know, it seemed a sin to do that, but I plan on getting the book bound again once I've colored all the pages.
At last count, she had 12 of them that are available on Amazon US. They come out in Sweden first, then they trickle onto different markets worldwide. The strange thing is that she draws a lot of bugs. I thought I could not color bugs for fear of nightmares (I tend to color really really late at night), but I actually enjoy them. They are usually bejeweled and bedazzled, maybe that is why.
Below are some of the pics I've colored. It's a shame really that I did not discover her books and overlooked the other challenges sooner.