Hypothesis: Owing to the entropic interactions between polymers comprising a blend and surfaces of colloids immersed in this blend, the polymer inter-phases are formed between the colloids and blend. These inter-phases that are non-uniform both in density and composition, mediate the effective interaction between colloids immersed in a polymer blend. We surmise that there is an additional non-osmotic mechanism of the polymer mediated interactions specific to polymer blends, which is caused by the compositional non-uniformity of the above colloid-blend inter-phases. Theory: By developing and making use of the random phase approximation based upon the Sanchez-Lacombe equation of state, we calculate the second virial coefficient of the effective interaction between colloids mediated by a polymer blend. The proposed approach takes into account finite compressibility of a polymer blend, as well as the specific (strong) interactions between dissimilar blend components. Using the obtained results, we derive the equation of state of a polymer blend filled with colloids. Findings: We prove that the correlations imposed by the variations of the composition of a polymer blend cause a significant contribution to the polymer mediated interaction between colloids immersed in this blend. This contribution dominates over the osmotic contribution in the case of dense polymer blends. (C) 2019 Elsevier Inc. All rights reserved.