I’m really into the “adult coloring” craze right now, and am always on the lookout for nice horse-themed books. This was one of the first I found, created by Christina Riley. It’s so awesome to see hobbyists releasing stuff like this!
She has two books called Horsin’ Around: Just Horses! and Horsin’ Around: Color Me Crazy! I purchased a copy of Color Me Crazy and have really enjoyed it so far.
The illustrations in this book are gorgeous and very well done. What I really love is the variety.
Some of the horses are tacked up…
And others aren’t.
There is also a nice variety of breeds, including a couple bonus zebras. 😉
The drawings in Color Me Crazy have had intricate backgrounds added to them, which are fun to color in. Also, all of the pages are printed on one side of the paper.
Here’s one of the pages I’ve completed:
Both books can be purchased directly from Christina here. She’s having a clearance sale on them right now, so if you’re interested I’d definitely recommend snagging one up!
More of her beautiful work can be found on her website, http://crileycustoms.weebly.com/ and Facebook page as well. 🙂
Desktop Stables 
I just recently added both of Christina’s books to my coloring book collection and you’re right – they ARE nice. I’m finding that I, too, am really ‘into’ the coloring book craze, especially horse themed ones!