A system provides light of selectable spectral characteristic (e.g. a selectable color combination of light), for luminous applications such as signage and indicator lights. An optical integrating cavity combines energy of different wavelengths from different sources, typically different-color LEDs. The cavity has a diffusely reflective interior surface and an aperture for allowing emission of combined light. Control of the intensity of emission of the sources sets the amount of each wavelength of light in the combined output and thus determines a spectral characteristic of the light output through the aperture. A deflector shaped like a number, character, letter, or other symbol, may be coupled to a similarly shaped aperture. By combining several such fixtures, it is possible to spell out words and phrases, with selectable color lighting. Disclosed fixture examples use an extruded body member with appropriately located reflective surfaces, to form both the cavity and deflector.