UV continuum slopes predicted by the spectral evolution model adopted in this work. We show model predictions for a constant SFH of different ages and three metallicities: ﹩\mathrm{log}Z/{Z}_{\odot }=-2﹩ (blue), −1 (green), and 0 (orange). Dashed lines indicate predictions for stellar emission only, while solid lines for stellar and nebular continuum emission. In this latter case, we consider a photoionization model with ionization parameter ﹩\mathrm{log}{U}_{{\rm{S}}}=-2.5﹩ and depletion factor ﹩{\xi }_{{\rm{d}}}=0.3﹩.