A grisaille is a painting which has been executed in monochrome (i.e. one colour) or in a very limited range of colour, but in which the forms are defined by variations of tone.
In Mantegna's 'Samson and Delilah' a grey grisaille is set against a fictive marble backdrop to give the illusion of a sculpture. By contrast, in Rembrandt's 'Ecce Homo', brown predominates; as this painting is a preparation for an etching, tonal variation is of primary importance. Boilly's painting of 'A Girl at a Window' wittily pretends to be a black and white print.
Grisaille painting was particularly popular for the outsides of the shutters of polyptychs in Northern Europe in the 15th and 16th centuries.