Have You Ever Seen a Smack of Jellyfish? An Alphabet Book by Sarah Asper-Smith uses contrast to enhance her illustrations.
This is an alphabet book that pays attention to grouping and not always the usual animal groups' name. For example the typical elephants in a group are a herd, but she says: "a PARADE of ELEPHANTS? The animals are black, like silhouettes and the nouns for the groups are in all capital letters and then the beginning letter of the animal is a different color to show emphasis and coloring matching.
Here is a link to a PDF that you can print out and color yourself from Have You Ever Seen a Smack of Jellyfish?
My best guess is that these illustrations were created digitally.
A refreshing addition to your alphabet books and you learn a little more about unusual animal group names. Even though it is an alphabet book, I would use this with children PreK to Third grade because they will be learning more unusual names for an animal group.