1. An optical unit for a spatial light modulator (SLM)-based color projection display system having a white light source, comprising: three SLMs, each operable to receive light of a different primary color, and to generate images of that color; a filter associated with at least two of the SLMs, each filter operable to filter the light from the source such that it provides one of the colors to that SLM; wherein the filters receive the light from the source in succession, such that each filter receives light not provided to an SLM by a preceding filter; and a projection lens associated with each SLM, each projection lens operable to receive the images generated by its associated SLM and to direct the images to a viewing plane; wherein each projection lens is a narrow band projection lens for light of the associated color; wherein the projection lenses are positioned such that the images from each projection lens converge at the viewing plane.