This study introduces a new model and a new mathematical formulation describing the light scattering and ink spreading phenomena in printing. The new model generalizes the classical Kubelka-Munk theory, and unifies it with the Neugebauer model within a single mathematical framework based on matrices. Results like the Saunderson correction, the Clapper-Yule equation, the Murray-Davis relation and the Williams-Clapper equation are shown to be particular cases of the new model. Using this new theoretical tool, the reflection spectra of 100 samples printed on high quality paper by two different ink-jet printers were computed with an average prediction error of about ΔE = 2.1 in CIELAB.