* To evoke the feel of early cinema. The story is set in the 1930s, a time when film was still relatively new and black and white was the standard. Selznick wanted to capture the gritty, nostalgic feel of that era, and black and white photography perfectly evokes that.
* To emphasize the interplay of light and shadow. Selznick's illustrations are masterfully crafted, using light and shadow to create mood and atmosphere. He uses them to highlight the characters' emotions and create a sense of mystery and suspense.
* To draw attention to the intricate details. The illustrations are incredibly detailed, with intricate patterns and textures. The lack of color allows the viewer to focus on the individual elements of each illustration, making them even more striking.
* To create a unique visual style. Black and white illustrations are not as common in children's literature, and Selznick's use of them helps to make his book stand out.
* To complement the narrative. The illustrations work in conjunction with the text to tell the story, adding another layer of depth and meaning. The use of black and white makes the illustrations feel more like cinematic stills, further enhancing the story's connection to cinema.
In short, Selznick's choice of black and white illustrations was deliberate and carefully considered. It was a way to enhance the story, create a unique visual style, and pay homage to the early days of film.