These changes in color of stones by the impregnation with methyl-trimethoxy silane were studied by using a color meter. With a higher amount of silane, the treated stone exhibited a greater color difference, mainly caused by the lowering of the value, and the changes of hue and chroma were negligibly small. After accelerated deterioration all the stones treated by the silane showed almost the same color as the untreated stone, while the hydrophobicity of the treated stones was found to be satisfactory.