Lionni uses earth tones in his illustrations that are close to the actual colors of the objects found in nature. In his book "Inch by Inch", for example, he uses realistic shades of brown and burnt orange in his collage of a robin, while the tree branches are shades of brown with dark green leaves. Mice are consistently found as characters in Lionni's books, such as the star character in "Frederick" and the title character in the Caldecott Honor Book "Alexander and the Wind-Up Mouse". Lionni's illustrations have been compared to those of Eric Carle as both often employ animals, birds, insects, and other creatures to tell a story about what it is to be human.