A system comprising: an optical display device arranged to create a perception of a sky scene in output light, and a determination system, the optical display device comprising: a diffuse light generation system; an output aperture for the output light, and; electrical circuitry arranged to control the output light, the diffuse light generation system arranged to generate a blue diffuse sky light component in the output light, the determination system arranged to determine a colour of a real-life sky light component of a real-life sky, which is determined separately from a colour of a real-life sun light component of the real-life sky, wherein the electrical circuitry is arranged to control a colour of the diffuse sky light component based on the determined colour of the real-life sky light component.