We see many adult coloring books in the bookstores these days, which are called art therapy books. It is probably an oversimplification of art therapy, but that is for another thread of conversation.
I purchased one of those books and started coloring with my daughter. I soon found myself not liking it because I have to only color where I am supposed to. All the lines were so thick and black. They were so definitive like I was not supposed to color outside those lines. I wanted to define where I can color and what the shapes are going to be. So this is my version of my own art therapy. This soothed me.