If you want a clean and bold look for your picture, you can use colored markers for the color. It has a wide variety of colors and you can choose between fine tipped ones and broad tips depending on your needs. There are also refillable markers where you can just purchase ink whenever it dries up or loses its color. It's also an easy material to use. You just have to apply a single coat on the drawing. You can also add some more details using either a white colored pencil or a white inked pen.
This art therapy trend has yet to hit America, but because publishers have found it immensely profitable, it's probably only a matter of time before you find yourself shopping for a new box of crayons. And hey, why not? Coloring is a fun and joyful activity that is a much easier way to reduce stress than, say, dragging yourself to the gym. It just might get awkward if your friends find your completely finished Benedict Cumberbatch coloring book.