Professional level pencils like Derwent or Prismacolor offer the best quality and typically are the most expensive pencils to buy. The wax in these pencils is softer and the colors are a higher pigment providing brighter colors. The soft application allows blending and shading.
As the Huffington Post points out, coloring books for adults are best sellers in France and the U.K. Hachette, a French publisher, has even capitalized on the trend by selling a 20_volume collection of stress_reducing coloring books called Art_Thérapie. Using coloring books to de_stress has been especially popular amongst French women, who have even taken to posting their creations on social media and forming Facebook groups to share coloring tips.