I have several adult coloring books now, I have been experimenting with printing them out on cheap printer paper as well as higher end watercolor paper. This image came from a very inexpensive coloring book found in the Dollar General stores, you will have to go back to the children's coloring book & puzzle books to find this one, it's called Coloring Cats & Dogs and it's published by Bendon Books.
There are 3 titles in this series, and they all run $3.00 each, yes that's right, they are that inexpensive. Yet the paper quality is pretty good, and they are printed one sided, meaning you can color on a page without worrying about bleed through messing up what's on the backside. If you are using a medium that really bleeds through, like markers, it's recommended that you put another sheet of something behind the page you are coloring.
I colored this page with Marco Raffine colored pencils, they come in a 48 and a 72 pack, I have the largest pack, unfortunately they are not available open stock, but they are inexpensive enough, especially compared to the higher end colored pencils that it will not break the bank to buy another entire set. These pencils are an oil based pencil (as opposed to a wax based), they lay the color down pretty well and they layer beautifully. You can blend these as well.
My approach to this picture was to lay down a layer of the lightest color first, then gradually going into the areas where there would be shadows and shading, I applied increasingly darker colors in the same color family, for example, going from a light yellow, to a medium, then to a near brown. I wanted even more contrast so I picked up the black pencil and colored in the deepest shadows and shading.
Since this lion had so much small details drawn in (doodle style), I chose to color in blocks rather than trying to color in the tiny details, I also used very strong and unnatural colors, I wanted to play with these vibrant colors instead of trying to use natural colors for a lion. You may notice the one spot on the left side of the mane that is slightly browner than the rest of the mane, that was where I had started a few days earlier and didn't keep up with the colors I was using, it also shows that I'm not perfect... but I am very happy with how this turned out. If you wish to see how I do this, let me know and I'll be happy to make a video tutorial on how I do this.
Enjoy, click the images to see them full size.