An illumination system and method is disclosed. In one example, the illumination system comprises a lamp assembly for generating color-variable light, a controller for generating control signals for the lamp assembly, source color input means, preferably a color sensor, for inputting to the controller information defining a source color; a memory associated with the controller, containing information defining at least one color harmony rule. On the basis of the input source color, and using the harmony rule from the memory, the controller calculates a target color and generates its output control signals accordingly. Thus, the light output from the lamp assembly harmoniously matches the measured color of surroundings or objects.