Using several theoretical approaches relying on the time-dependent density functional theory, we have computed the electronic spectrum in the visible range of a squaraine dye, either isolated or embedded into a tetralactam macrocycle. The amplitude of the bathochromic displacement induced by the complexation is well-reproduced by the most accurate models. This total shift is split into specific components, allowing us to unravel the most-important contributions (geometry modifications, polarisations...). This study constitutes a further step in the investigation of environmental effects on dyes' absorption spectra.