The difference in appearance of eight artist's colors under a number of illuminants at different illuminances is investigated. The sources tested include daylight fluorescent lamps and incandescent lamps. The Munsell color corresponding to each of the eight pigments viewed under one of the sources under test is found. The pigments are then matched to a second Munsell color under the other test illuminant. The differences in color are plotted on a Munsell color diagram and calculated in Commission Internationale de l'Éclairage L*, a* and b* (CIELAB) units. The greatest color differences were found between daylight at 10,000 lux and incandescent light at 150 lux. The authors conclude that incandescent lamps may not be suitable sources for the exhibition of works of art which were painted before artificial lighting became generally available. It is suggested that for best color rendition paintings should be viewed under north-sky light or a simulated daylight. It is suggested that the large color differences calculated provide an explanation for metameric retouching. Finally, it is pointed out that fluorescent lights change the appearance of colorants to a lesser extent than incandescent lamps when these sources are tested against daylight. -- AATA