Duotone
An image printed or displayed in two colours, usually one dark and one light or bright.
Also: two-colour print
A duotone was originally a way of printing a black-and-white photograph with two inks, such as black and a warm brown, to give richer tones than black alone. Today the term more often means a picture in which the dark areas are mapped to one colour and the light areas to another, for instance deep blue shadows and hot pink highlights. The style is striking and cheap to print, and it lets very different photographs look like a set. It has been popular in posters and music streaming graphics.