Duotone

[1] This is most often used to bring out middle tones and highlights of an image.

Traditionally the superimposed contrasting halftone color is black and the most commonly implemented colors are blue, yellow, brown, and red, however there are many varieties of color combinations used.

[2] Due to recent advances in technology, duotones, tritones, and quadtones can be easily created using image manipulation programs.

A fake duotone, or duograph, is done by printing a single color with a one-color halftone over it.

[3] This process is generally not preferred over a regular duotone, as it loses much of the contrast of the image but it is easier and faster to create.