Solvent effects in the electronic spectra of a cyanine dye (1,1′-diethyl-3,3,3′,3′-tetramethylindocarbocyanine, diIC2(3)) were studied. Solute/solvent interactions originate from dispersion forces but contributions arising from the solvent Stark effect were also detected, showing significant changes of both dipole moment and polarizability of the dye on the electronic transition. The absorption and emission spectra of diIC2(3) in glycerol at different temperatures were obtained and analyzed in the framework of the coordinate configuration model, caused by the slow solvent dynamics. It is shown that this model describes the dye thermochromism at high temperatures well, but the internal nuclear coordinate plays an important role at lower temperatures.