The commercially available Chelsea filter is used to differentiate and characterize a variety of artist's paint pigments. The filter transmits in two narrow separate regions of the visible spectrum: a band of yellow-green light centered at ~ 550 nm and a red light of wavelengths greater than685 nm. Other regions of the visible spectrum are heavily absorbed. With transmitted illumination using white light through the Chelsea filter, select blue and green paint pigments exhibit anomalous colors. Most notably, ultramarine blue appears a deep red and smalt appears a rose red. The latter can be easily differentiated from prussian blue which exhibits only a dull gray green. Certain imitation terre verte pigments can also be readily detected by the anomalous red appearance. Photographic documentation of this effect requires film with appropriate spectral sensitivity. Ektachrome® slide film was found to be unsuitable for this purpose because of its relatively sharp and narrow characteristic curve for the red-producing emulsion layer. Kodachrome® slide film has a broader characteristic curve and documents the effect very well. Although transmission spectra of individual particles would also allow differentiation and characterization of the pigments, the Chelsea filter allows rapid scanning of preparations, is simpler to use, and is less expensive. To apply the technique more generally, an illuminator was constructed allowing a combination of two different filtered light paths.