A purple pearl sample of Pinctada martensii, which shows color anomaly, was tested by means of synchrotron radiation X-ray fluorescence spectra, ultraviolet-visible spectra and Raman spectra, with the purpose of studying its color-forming mechanism. The results show that the purple pearl sample of Pinctada martensii was dyed on both surface and nucleus by inorganic dye, and hence its color is dyed.