The illustrations by Caldecott Medalist Beth Krommes are the main draw of this book. The text is a fairly simple poem, but the pictures tell a full story, portraying the little girl's fear as the thunder begins, and her joy at being able to play in the mud, as well as the reactions of the baby, dogs, cat, and other animals to the abrupt changes in weather conditions. There are many details that can only be appreciated through careful observation - the farmer's hat blowing off as the wind comes up, turtles and fish lurking beneath the surface of a pond, and the cat begging to be let out, then joining the horses in the barn. The animals also make great faces. I especially love the look on one of the dogs when he discovers a frog and the contrast between the pigs' wide eyes when it's raining and their contented smiles when they can lie down in fresh mud. Only one thing bothers me - a boat with a person in it appears early in the story, and we see the boat tossed in the waves as the storm strengthens, but at the end of the story, only the boat is accounted for (safely moored outside the bathroom window), not the person. Where did he or she go? I'm tempted to email the illustrator to ask.
Blue on Blue is a wonderful lap book. My toddler spends a lot of time just poring over the pictures, pointing at everything and asking for me to label it. The animals make it especially appealing to her, as most of the words she knows right now are animal names and sounds. The book is very similar in style to Krommes's Caldecott Medal winning book, The House in the Night. In fact, her portrayal of a night sky in this book is identical to how she portrays it in The House in the Night. Textually, and thematically, it's a nice read-alike for All the World (though not quite as well-written) and it would also be interesting to pair with Tap Tap Boom Boom to explore how rain affects life differently in a city and on a farm.