A special variant of dark field illumination in which transparent, coloured filters are inserted just before the condenser so that light rays at high aperture are differently coloured than those at low aperture is known as

Rheinberg illumination is a special variant of dark field illumination in which transparent, coloured filters are inserted just before the condenser, so that light rays at high aperture are differently coloured than those at low aperture (i.e. the background to the specimen may be blue while the object appears self-luminous red).