It is intended to be possible to use a respective setting apparatus (E1, E2) to set the color and the brightness of an illumination device separately. Light sources having three different colors are operated for this purpose. Only one first power supply (CON, PWM1) is provided for two colors, whereas the third color is supplied by a second power supply (CON, PWM2). The brightness can be set by altering the power output of the first (CON, PWM1) and the second (CON, PWM2) power supplies at the same time. The color can be set by altering the power output of the second (CON, PWM2) power supply.