Logarithm of the estimated τ for the sample bulges (left-hand side) and disks (right-hand side) vs. observed optical colours (g − i in the first row and r − i in second) after correction from intrinsic extinction effects, mean stellar age (mass-weighted in the third row and luminosity-weighted in the fourth), and EW(Hα) in the fifth row. Observations (defined by the circles) are contrasted with the model predictions (illustrated by the stars).