A comparison study was made between the yellow and white nacre of the gold-lipped Pinctadamaxima oyster shell and 65 yellow cultured pearls, both natural and treated color, produced from this mollusk. The yellow nacre of this shell has a characteristic absorption feature in the UV region between 330 and 385 nm; the strength of this feature increases as the color becomes more saturated. White shell nacre fluoresces very light blue or very light yellow to long-wave UV radiation, whereas yellow shell nacre fluoresces greenish to brownish yellow or brown. Natural-color yellow cultured pearls from P. maxima exhibited absorption and fluorescence characteristics similar to those of the yellow shell nacre. In contrast, the absorption feature in the UV was either weak or absent in yellow cultured pearls reportedly produced by a method involving heat treatment, and their fluorescence was generally very light blue or light yellow.