The invention provides an ambiance lighting system for a vehicular passenger compartment comprising a variable color light output which is automatically responsive to temperature changes. First and second light sources of different colors (e.g., blue and red) are positioned immediately behind the air discharge vents and are selectively energized by a control circuit so that the first light source radiates light through the vent when the temperature falls below a predetermined value and the second light sources energizes the second color of light when the air temperature rises above a predetermined value. Sensors are used to detect the temperature of air, preferably in the ducting plenum. Various control strategies can be deployed to achieve aesthetically interesting light presentations which enhance ambiance within the passenger compartment.