The ONE COLOR Books series is the most stress-free coloring you'd ever tried! No thoughts. No extra skills. So fun and easy to color! Color the attractive magic LINES with just ONE COLOR of pen, pencil or marker to get 25 amazing pictures with animals. For better results use dark colors. Listen to the radio, your favorite music or audio-book and enjoy your internal harmony while coloring. This is the perfect book to take on the go as it is of the letter-size format and lightweight. Relax just with one color! The series includes these coloring books: