Contrast will make a room feel smaller. The less contrast there is in the room decor the larger the room will be perceived. A monochromatic color scheme will produce a room that feels much more spacious than one with a myriad of colors. A graphic example of this is the comparison of a Victorian style and a monochromatic living room of similar size. The high contrast room will appear smaller.
Items further away tend to appear darker. A wall painted a darker shade of the same color as the adjacent walls may appear further away, thereby making the room appear longer. A shade of color is achieved by adding black to the paint color. If any items are placed on the wall, such as furniture or pictures, these items will force the wall back into perspective, and the illusion of depth may be lost. If, however, the items are the same color as the wall, the contrast is minimal, and the illusion of depth is maintained.
If the wall is painted a color that is different from the adjacent walls, and a color shaded darker than that of the surrounding walls, the contrast will force the wall to appear closer, to come forward. That which is different will be perceived first and therefore be the most prominent. The room will then appear shorter.
The quality of the wall finish will also influence the perceived depth of the room. Painting the wall a flat finish will diminish light reflection, and the wall will appear further away, regardless of the color. Directing light away from the wall will also add to the illusion of depth. Floor lamps and table lamps directing light downward will also decrease the visual weight of the wall.