A monochromatic color scheme is not necessarily a neutral gray picture. It can be composed of any single color taken through the full range of values from light to dark.
There is long tradition for artwork for made only in grayish or brownish tones (Above, F.R. Gruger). Any drawing tool, such as a pencil or a stick of conté crayon, automatically makes a monochromatic image. Painters have rendered figures or scenes en grisaille, which literally means “in grays.” Grisaille painting was most often used as a preliminary step to work out the tonal values, or as a part of the process in painting, before the colors were overlaid in transparent glazes.
But apart from those exceptions, most painting through history has been created in full color. The 19th century and early 20th centuries saw the invention of several imagemaking technologies, including photography, halftone printing, motion pictures, and television, all of which began in black and white. It took until well in the 20th century before all those media changed to full color. The New York Times didn’t run a color photo on its front page until 1997.
As a result, people living through the early part of the last century got used to seeing the world interpreted in black and white or sepia tones. Now, of course, full color is universal, and black and white has become artistic choice rather than an economic one. Monochromatic schemes often draw attention for their very uniqueness and understatement.
Today in graphic novels or illustrated books, monochromatic schemes immediately suggest historical photos, as in this image Dinotopia, to lend credibility to an imaginary world. In full-color comics, flashback sequences are often presented in sepia.
In a painting, you can lay out any string of grey, brown, or blue colors. If you want to simulate an old photo, it often helps to stop short of the full range of tones. Instead of a black or a bright white for the extreme values, a more limited range can better suggest a yellowed or faded photographic image.