The ceiling, the side wall, and the floor form the background of the room against which all the furnishings and the occupants of the room are seen. Like the frame of a picture, the background should be subordinate in color as well as in amount of detail. This limitation, far from minimizing the importance of the background, gives it an added distinction, and demands for it the most careful consideration. The function of the background is to serve. While not obtruding itself, it should through its color supply a pervading influence that may be felt like an atmosphere. This province of the background is best filled, as has been said in the discussion of color, by subdued warm colors, not too dark, that harmonize with the more usual types of furnishings and methods of lighting. (See Plate III.)

Ceiling, side walls, and floor are parts of one whole. They should, therefore, be keyed to the same color. This important point has often been disregarded. The ceilings have been made white, the floors constructed of any convenient wood without reference to its color; the color of the walls has been chosen without reference to either floor or ceiling. In the distribution of color values in the background, the old analogy, often repeated, holds good: the side walls of a room correspond in value to the middle distance in a landscape; the ceiling corresponds to the sky which is lightest of the three; the floor to the ground, which is the darkest. This is not a mere fancy. A very dark ceiling or sky is threatening and oppressive in effect. The dark tones of the ground contribute to an effect of stability and support that are fundamental in a serviceable floor.