Often used as a "trip down memory lane" effect, this occurs in film or TV shows (usually referencing a film) when wishing to confer an obvious stylistic nod to the black-and-white era of moviemaking upon the audience. A simple trick, the saturation (colour) of the effect is slowly drained until the picture is completely monochromatic or grey, just like all those Film Noir pictures of the 1940s and 1950s. The effect can also be used more subtly, with only a slight change of hues and saturation to simulate the effect of a dream (fuzzy edges), fantasy (usually with a cloud) or flashback sequences as required. Also done in reverse.