The paper presents an innovative approach to the spectral-based characterization of ink-jet color printers, managed here as RGB devices. Our objective was to design a separation procedure based on the inversion of the Yule-Nielsen modified Spectral Neugebauer model. To improve the performance of the direct model in computing the reflectance spectrum of the print, we designed a method that exploits the results of its numerical inversion to estimate a correction of the amount of black ink computed on RGB values. Using our method, we were able to faithfully characterize an ink-jet printer by measuring a chart of about 100 colors.