Purchase 10 ISBN numbers from Bowker's. Ten is the fewest numbers you can buy. You will be able to save the extra numbers to use on subsequent self-published coloring books. Once you designate an ISBN number to identify a book, it cannot ever be used on any other book or even on other versions of this book.
Produce a digital version of your coloring book. Scan each illustration using a digital scanner. Save the scans as jpeg files. Open a contiguous file for the body of the coloring book. Make the first page the title page and put the copyright symbol followed by the year. If it is in the last quarter of a calendar year, it is permissible to list the copyright date as the next year. Use text boxes and the jpeg files to format each page. Add page numbers at the bottom in the center of each page.
Create a cover for your coloring book using a separate file. The front cover should have a catchy illustration, perhaps in color. It should also feature your name as the author and illustrator. The back cover usually contains promotional text as well as information about the price and the ISBN number.
Decide whether your self-published coloring book will be produced as an e-book or as a paper coloring book. To make an e-coloring book, use a PDF creator to save the book. If you plan to have your coloring book printed, there are even more choices. You can take the electronic files of your coloring book to any printer who will be able to make copies and bind them. Usually the price goes down as the number of copies goes up. You can contract with a print-on-demand publisher to make a certain number of copies and more as you need them. Some print-on-demand publishers also offer marketing and sales fulfillment services as an option.
Promote your self published coloring book using press releases, posters and postcards. Announce the availability of your coloring book online at your website, blog and on as many social networking forums like Twitter, Facebook and Myspace as possible. Try to get speaking engagements where you can sell copies of your coloring book to your audience. Arrange for your coloring book to be sold in stores and wherever else they would make sense. Sell your coloring book online at eBay, Amazon, and on your own website. Get people to review and recommend your coloring book. This part of self publishing a coloring book---getting people to learn about it and buy it is the most challenging part. It takes a different set of strategies than the artistic, creative ones that you used to produce the coloring book. You may find it useful to contract with a sales representative or a distributor to get your coloring book into many different prospective markets and catalogs.