A Variety of Pressure Creates Emphasis. If there are some areas you want to accent, you can press a little harder on the crayon and end up with a darker, more intense color. This is another good reason to color lightly for full coverage. For example, in this picture of the heart below, I pressed harder when tracing the lines within the heart and in the vein and artery openings. I did the same thing when coloring the muscles and the brain.
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.