An achromatic or neutral color is any color that lacks chromatic content, including white, black, and all grays. Near neutrals include browns, tans, pastels, and darker colors of any hue or lightness. Neutrals are achieved by mixing pure colors with white, black, or gray. Black and white combine well with almost any other colors – black reduces the saturation or brightness of the color paired with it, while white shows off all hues to equal effect. In color theory applied in interior design, neutral colors are those that are easily modified by more saturated colors next to it, so that the neutral color would appear to take on the hue complementary to the saturated color. When a bright red sofa is placed in a room with a gray wall, the wall will appear distinctly greenish.
via Architectural Digest