A novel color characterization method for general colorful inkjet printers is proposed. The method investigates the printer color separation and medium color rendering processes, based on which spectral reflectance can be predicted. The Yule-Nielsen special Neugebauer (YNSN) and enhanced YNSN models, which are based on simple and complicated dot gain respectively, are employed in the printer color separation process. As the color separation cannot be directly controlled, the colorimetric error objective function is designed. The mapping between RGB and CMYK is modeled using polynomial regression, and is resolved by nonlinear optimization. Experiment results show that the proposed method can characterize the color printer accurately. In comparison with existing techniques using simple color separation model, the proposed method produces improved colorimetric accuracy.