The formation of supramolecular aggregates of anthraquinone dye N,N'-(4-methylphenyl)-1,4-diaminoanthraquinone (AQ) is shown to be clearly manifested in temperature-dependent selective reflection spectra of cholesteric solvents containing AQ as a non-mesogenic dopant. Using cholesteric matrices of different chemical nature (based on cholesterol esters or nematics with chiral dopants), one can distinguish between interactions of a solvent with individual AQ molecules and AQ aggregates, as well as between the aggregation and precipitation of AQ. The calculated relative birefringence data demonstrate the effects of AQ aggregates on the optical anisotropy and the orientational order in. the systems under study.