Blue Star Coloring has published a series called Adult Coloring Books: Stress Relieving Patterns and they are very popular. The first book has 46 illustrations, one per page (so the back is blank), and the paper is medium weight. The designs range from simple to very complex. I recommend placing one or two sheets of blank paper under the page to be colored in case of bleed-through.
There is already a second volume in this series, Adult Coloring Books: Stress Relieving Patterns Vol. 2, and it continues in the same vein. There are 54 illustrations, one per page, and the patterns vary from floral to geometric. Again, there can be a problem of bleed-through if you are using gel pens or markers.
The third book, Stress Relieving Kaleidoscope Patterns, has 30 kaleidoscope patterns with symmetries and fractal forms. And the fourth book, Stress Relieving Paisley Patterns, is intended for advanced colorists. There are 38 paisley-inspired designs that are more intricate and convoluted to color. Again, a blank piece of paper should be inserted behind the drawings if you are using markers or gel pens, to avoid bleed through.
