On my website learning page is an article on the importance of image neutrals. This is a brief argument as to why you should read the article and pay attention to the concept.
The eye is adaptive when it comes to color. The camera is not. Our brain interprets the visual signals we receive and uses key elements in the field to decide what colors things are. Key among those elements are neutrals, especially whites and blacks. The photographer presents an image to the viewer that is not viewed as a normal scene is viewed. It is viewed in the context of the environment it sits in, including the frame and mat.
Since our brain has already established a reference for color, even in the context of a dark room with a projected image, the colors in the image are relative to that baseline. To convince a viewer that the colors in the image are accurate, or intentional on the part of the image maker, a neutral should be present in most images. There are always exceptions, but those should be obvious. The presence of neutral tones in the image signals the viewer that the other color values of the image being viewed are to be accepted as legitimate values.
If the image lacks neutral values the viewer’s brain becomes “suspicious” of the color in the image, suspecting a color cast or wondering if the subject in the image is really that color. This is not an obvious conscious conclusion, more an unsettled impression of the image content that subtly influences the validity of the image. The intention of the photographer is to have the image accepted by the viewer on many levels, artistic, compositional, and so forth. Establishing a neutral base in the image removes one negative element in the journey toward visual acceptance of the image on the part of the viewer.
Even if the colors are artificial or manipulated for an artistic purpose, the presence of a neutral allows the viewer to accept that the photograph is visually intentional. With this in mind I attempt to establish a base neutral in the darkest portions of all images, however small, that signals the viewer that the color and tone of the image are acceptable and intentional. That is simply the way the eye perceives color, and images that reinforce that perception are easier to view and accept.