A luminaire includes a white light LED light source emitting a light beam that that is filtered by first and second color filters. An optical device modifies the filtered light beam. A control system receives a commanded value for the optical device and responds by causing the optical device to move based on the commanded value; determining a Duv change in the light beam caused by the optical device; determining positions for the color filters based on the Duv change, a current correlated color temperature (CCT) isotherm value, and a current Duv value; and moving the color filters to their determined positions. The control system may alternatively receive a command with a Duv value and respond by determining color filters positions based on the received Duv value and a current CCT isotherm value; and moving the color filters to their determined positions.