The colored paintings of Changshu Caiyitang are outstanding representative of the architectural color paintings from south of the Yangtze River. However, some of the painting colors did not correlate with the colors in some traditional patterns. In order to identify the blue pigments, a comprehensive study employing microscopy, laser Raman spectrography and Xray fluorescence analysis were done;included in this study is prior preliminary work. The results show that a blue organic pigment (indigo) and a mineral pigment (azurite) were both used in the Caiyitang color paintings. Only indigo, used as a background color, was preserved, resulting in an apparent mismatch with colors in traditional patterns.