SBF-colours and integrated-colours measured for NGC 4621 (left panels) and NGC 4374 (middle panels), compared to the SPoT models from Raimondo et al. (in prep.). Black symbols mark observational data for the various annuli as labelled (triangles for NGC 4621, squares for NGC 4374). Measures within regions hosting SNe, and the measure for the main annulus for both galaxies, are shown in right panels: NGC 4621 and its SN Ia (SN 1939B) are shown with full and empty triangles, respectively; NGC 4374 and its SNe Ia (SN 1957B, and SN 1991bg) are shown with full and empty squares, respectively. For the models, different  [Fe/H] are indicated with different symbols ( [Fe/H] =  −0.7, –0.4, 0.0, +0.4 dex with three, four, five, and seven pointed stars, respectively). Larger symbols indicate older ages, from 4 to 14 Gyr in 2 Gyr steps (See electronic version of the Journal for a colour version of the figure).