To remain consistent with the story's simplicity, Freeman keeps the illustrations extremely literal. If the page says, "Corduroy watched them sadly as they walked away," we see Corduroy sadly watching Lisa and her mom walk away. If the page says the night watchman "came dashing down the escalator," we see him doing just that.
The pictures show readers exactly what's happening at that moment in the story—nothing more, nothing less. The lack of surprise "Easter egg" elements might make Corduroy less visually interesting for the adult readers, but it's perfect for directing the focus of young listeners who are still learning what a story is in the first place.
While many children's books feature almost cartoonish pictures, Freeman and his editor, Annie Duff, made a deliberate choice to keep Corduroy's illustrations realistic. Knowing that Black characters were still rare in children's books, Duff encouraged Freeman to model Lisa after an actual child "to avoid the slightest suggestion of caricature." (Source)
(Psst: check out our Best of the Web section for more info on the real grownup Lisa, who's every bit as awesome as the character.)
Of course, social commentary aside, this is still a children's book, so Freeman uses a wide palette of bright, vibrant colors to tell the story. Cheerful hues of pink and yellow dominate the pages when the department store is open during the day, while cooler shades of blue and black settle over the store at night.
Realistic doesn't mean boring in a world where teddy bears come to life.