Quality Matters. Not all colored pencils are the same. Cheap colored pencils tend to have harder wax leads and less pigment which mean they produce less vibrant colors and have a tendency to leave some white spaces uncovered in the grain of the paper. Because the lead is hard, cheaper pencil leads often have a tendency break and if the lead breaks throughout the length of the pencil you can be left with something that is unusable.
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.