The process of subtractive color mixing is beautifully demonstrated, and explained with marked clarity, by this apparatus. It is convenient to use before a large class and will serve equally well in a brief prsentation or a comprehensive lecture. The device consists of a metal cabinet containing a permenently installed plastic window panel in its inclined front surface. This window is uniformly illuminated from within the cabinet by a source of white light. Two clear openings are in this panel; the upper containing an illuminated coordinate system for superposing spectrophotometric curves (percent transmittance vs wavelength), the lower providing an illuminated area fro superposing two partially overlapping filters. A color bar of the complete visible spectrum extends across the panel just below the coordinate system and is matched to the wavelength scale.