In many cases, black is used for the foreground color, for example charcoal in drawing. If the background of such a picture is white, the resulting picture is black-and-white, or greyscale. If the background is some other color (e.g. brown), the image is no longer black-and-white or greyscale, but it is still monochrome.
Alternatively, it is also possible to create a monochrome image by using an arbitrary foreground color on a white (or seldom, black) background. Generally, when used on white paper, dark colors are preferred to give a sufficient contrast, such as brown (sepia ink, vintage photography) or blue (e.g. cyanotype; see also blueprint).
Monochrome in painting
Monochrome in computing
In computing, monochrome monitors display images in only two colors, usually black on white (technically, white on black), amber on black, or green on black.
How to create a monochrome image
An image, e.g. a photograph can be digitally tuned into monochrome by first converting it to greyscale and then applying a filter that changes the chrome, giving it the former grey tones a hue. There are many different ways to do that; with Photoshop, good results can be achieved using the Curves tool: this allows leaving the whites white and the blacks black, preserving the maximum contrast, and only alters the chrome of the greyscale shades in between.