For beginners I would suggest either the Staedtler or Faber Castell brand of pencils. These produce significantly better results than bargain bin pencils, provide good colors and allow you to try some simple shading and blending techniques. With practice the best coloring results can even be achieved with the most modest tools!
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.