The effects of heat treatment, dyeing treatment with organic or inorganic dyes and Co60-γ ray irradiation treatment on the reflection spectra of freshwater or seawater cultured pearls and shells were comparatively investigated mainly by UV-Vis diffuse reflection spectrometer, respectively. The results show that: (1) these three different kinds of treatment have a clear common effect on the absorption peak of 280 nm in the reflection spectra of the nacre of pearls and shells. Furthermore, the absorption located at 280 nm is attributed to the organic matrix, which is one of the important components of nacre from pearls, and it is not directly responsible for coloring of colored pearls. (2) It is clearly seen that the intensity of the above absorption peak gradually reduces until it disappear with the increase of intensity of different treatment process. Furthermore, the intensity of the main wavelength of the reflection peak weakened gradually in the ultraviolet region of diffuse reflection spectra, and red-shifted toward the visible light. To sum up, this present study may provide the basis and theoretical support for the investigation of the coloring mechanism and identification of pearls and the corresponding treated ones.