It's super popular nowadays for some reason
People say that it helps to de-stress you, that's a good thing!
What you need:
Any coloring medium of your own choosing
Uncolored drawings with sweet lineart
Here's a few links or pictures to get you started, they should be free to use:
Blizzard Coloring Book
Leonie Dawson coloring book "Creative Soul" edit: Pdf book download,100++ pages
Mandalas by WelshPixie (Del)
So get out of here, get some coloring done and post them in here folks