The main purpose of this work is to analyze the microscopic feature of solvent systems resulting from the basis of binary mixtures formed by a protic molecular solvent (methanol, ethanol, propan-1-ol, propan-2-ol, and 2-ethoxyethanol) and a 1-butyl-3-methylimidazolium (bmim)-based ionic liquid (IL) cosolvent composed of different anions (tetrafluoroborate, hexafluorophosphate, chloride, and bromide). At the same time, a complemantary aim is to evaluate the incidence of anion type on the solvation pattern. The empirical solvatochromic parameters E-T(N), pi*, beta, and alpha were determined from the UV-vis solvatochromic shifts of adequate probes. The behavior of the solvent systems was analyzed according to their deviation from ideality. E-T(N) polarity and pi* dipolarity/polarizability exhibit positive deviation from ideal behavior in all binary mixtures at the explored compositions. Moreover, E-T(N) and alpha parameters display synergetic effects in some binary mixtures composed of tetrafluoroborate and hexafluorophosphate anions. The influence of anion nature on the response patterns is clearly manifested in the basicity beta and acidity alpha of the media. This is connected with the degree and type of interaction between the anions and the 1-butyl-3-methylimidazolium cation. The ion-pair character of the ionic liquids affects their interactions with a solute or a molecular solvent. The application of an appropriate preferential solvation model allowed us to obtain valuable information about solute-solvent and solvent-solvent interactions of the selected ionic liquid mixtures. It is possible to identify relevant mixtures paying particular attention to the most remarkable microscopic properties, the acidity and the basicity, in order to propose "new solvents". Thus, the solvating feature can be tailored selecting the molecular and/or the ionic component at a particular composition. A simplified combined nearly ideal binary solvent/Redlich-Kister (CNIBS/R-K) equation is shown to satisfactorily predict the solvatochromic parameters within [protic molecular solvent + bmim-based IL].