A cassette containing a gel scroll is releasably attached to the forward portion of a housing of a luminaire. A light path through the cassette is aligned with a light exit opening of the luminaire. A gel scroll is wound upon a pair of drums in the cassette and intersects the light path. The drive motor for the cassette is contained in the housing of the luminaire. A drive system for the drums includes a driven member in the cassette that engages a drive member of the luminaire driven by the motor when the cassette is mounted on the luminaire. A fan in the luminaire moves cooling air through the cassette when the cassette is mounted on the luminaire.