The fundamental cause of the Yule-Nielsen effect, also called Optical Dot Gain, is the lateral scattering of light in paper. The lateral scatter of light can be described quantitatively by a point spread function, but a simpler model based on mean level scattering probabilities, P_ij, for scattering of light from region i to region j, has been used to describe the Yule-Nielsen effect in terms of the sum of three, rather than two, reflectance factors. The three reflectance factors are (1) the reflectance of the ink, R_i, (2) the reflectance of the paper, R_p, and (3) an apparent reflectance factor for a third component in the system, RCL. The nature and origin of the third component is modeled and shown to fit both tone and color behavior for an example halftone system.