Comparisons between integrated spectra and regions sensitive to the MPs effects. Left panel: model SSPs. Gen.1 indicates models with the standard mixture of the first generation, i.e. α-enh. Gen.2 represents the modified mixture of the second generation, i.e. α– and Y–enhancements and ΔCNONa (it also considers the CN–ONa abundance variations). The iron abundances are indicated in the texts in the right panels. Right panel: residual flux between the first- and second-generation spectra for each iron abundance. The wavelength regions affected by the chemical variations typical of the second generation are shown, corresponding to changes in the CH/OH/NH and CN bands and to the Na D line strength. The coloured lines indicate the blue and red continua bandpass intervals that correspond to the central bandpass areas of the same colour.