Fines play a very important role in the papermaking process and paper properties. High-yield pulp (HYP) contains a large amount of higher specific surface area fines, which may lead to the absorption of more dye at the wet end section. Better understanding of the dye fines interaction will help improve the dye efficiency in HYP-containing furnish. This study was focused on the fines from high-yield pulp and hardwood bleached kraft pulp (HBKP) on optical properties, particularly on the CIE (Commission Internationale d'Eclairage) whiteness and b* (negative values indicate blue, and positive values indicate yellow). The characteristics of both HYP fines and HBKP fines were presented, and their effects on dyeing (color-shading) process were investigated. Fines have a higher specific surface area and more dissolved and colloidal substances (DCS) than do the fibers. It was found that for a system made of HYP fibers, HYP fines had a negative effect, while HBKP fines had a positive effect on the color shading process. For a system made of HBKP fibers, a low content (5%) of HYP fines can increase the dye effectiveness, although when the HYP fine content increased further, the dye performance showed a decrease; HBKP fines retarded the dye effectiveness for the HBKP fiber system. For the mixture of HYP fines and HBKP fines, the turbidity measurement was used to explain the interactions between the HYP fines and HBKP fines. The dyes and HYP fines can form complexes, which then retain in the fiber network, thus improving the dye effectiveness and resulting in a higher CIE whiteness and lower b* of the paper sheets.