KN spectra comparison between the three different models, generated through the POSSIS code and calculated at 40 Mpc of distance. Each row represents a different time epoch: 0.5 d, 1 d, 1.43 d, respectively. The columns identify different KN ejecta compositions: on the left column, the spectra of panels (a), (c), and (e), are generated by an opacity contribution of 100% of Se. The right columns, (b), (d), and (f), are calculated by considering Se at 10%, and a grey opacity of ${\kappa }_{\mathrm{grey}}^{\mathrm{mix}}=0.5{\mathrm{cm}}^2{\mathrm{g}}^{-1}$ for the remaining 90% of the composition. In the last epoch, we also included the AT2017gfo spectrum for a consistent comparison in the analysis.