The Artist Who Painted a Blue Horse by Eric Carle was named one of the best picture books of 2011 for many reasons. I like it because it teaches colors and reinforces creativity in preschoolers. The book doesn't follow the traditional color patterns making a horse brown and a crocodile green. This enables children to see the color first and then the animal. It's also a lot fun, especially when the kids get to tell you how wrong you are!
Here are some coloring sheets to go along with this book.
Here is a link to the book on Amazon