The photobleaching of the Monascus anka red pigments N-glucosylrubropunctamine (3) and N-glucosylmonascorubramine (4) by sunlight irradiation in aqueous solutions at pH 2.8 and 6.0 is substantially inhibited in the presence of 1,4,6-trihydroxynaphthalene (10). This protective effect is specific with respect to the number and position of the hydroxyls in the naphthalene ring and seems related to the ability of 10 to form molecular complexes with 3 and 4. Fermentation processes for the production of natural products from microorganisms are central to the needs of the pharmaceutical and food industries in terms of drugs, additives, nutrients, and processing aids (Arima, 1977; Woodruff, 1980). The genetic manipulations of useful microbes through the induction/selection of mutants and the use of DNA recombination techniques (Elander, 1980) will continue to improve the capabilities and efficiency of fermentations. Against such promising technological background, the available information of the potential of microorganisms as color producers contrasts as fragmentary and superficial. A recent compilation of microbial metabolites (Laskin and Lechevalier, 1973) lists pigmented products whose color, however, is secondary to some significant bioactivity, as in the case of antibiotics, toxins, carcinogens, fungistatics, antitumor compounds, etc. The systematic search for nontoxic, bioinert microbial pigments that could function as food additives is yet to be realized. One important application for food colors is the area of liquid formulations like carbonated beverages, canned fruit juices, and the like. For that end, it is particularly important to establish their colorfastness in solution, as affected by light, pH, and temperature. In this paper we discuss our observations on the protection of the red pigments rubropunctamine (1) and monascorubramine (2) against sunlight fading in solution.