If you want to teach the term diversity, you should read Ashley Bryan's All Things Bright and Beautiful. In illustrating Cecil Frances Alexander's hymn with richly colorful endpaper, Bryan gives us several visual examples of diversity. We see a diverse selection of children from around the world. There is a varied group of animals represented in the book. Different landforms and weather patterns also populate All Things Bright and Beautiful. The most noticeable example of diversity is in Bryan's use of color. It's like a Crayola box of 64 crayons exploded on each page. This amazing display of shape, size, and color illustrate Bryan's theme of our world being a wonderfully made planet with a richness of life in all four corners and all four seasons.
If you want to read a book to help explain how illustrations can carry a main idea, this would be a good choice. Each page resonates with a diverse landscape. You can see by the cover that it is a gorgeous book. This would also be a great book for working with a preschool audience since there is so much information contained in the illustrations.