Spectra for models with and without shells of ⁵⁶Ni in the outer ejecta. Left: spectra are shown for 1.50 d after explosion, which corresponds to during the flux excess phase. All spectra have been binned to Δλ = 15 Å. We note that the spectrum of our fiducial model has been artificially scaled in flux by a factor of three. Right: spectra are shown for 18.75 d after explosion, corresponding to close to maximum light. All spectra have been binned to Δλ = 10 Å.