Comparison of the SED of a 13.7 Gyr old bulge (τ1 SFH model) that is simulated at z = 1.64 (corresponding to a cosmic age of 4 Gyr; red) with a 4 Gyr old SED for the same SFH and redshift (blue). To ease a comparison, the 13.7 Gyr old SED has been shifted by +0.83 mag to match the 4 Gyr old SED at the rest-frame wavelength of 4100 Å. It can be seen that, whereas these SEDs do not strongly differ from one another in their slope for λ > 1 μm, they do so in the ObsF optical where the 4 Gyr old SED is by a factor of ∼5.8 brighter than the 13.7 Gyr old SED. This example illustrates the significant difference between k corrections computed in an EvCon manner and those based on SED templates with a fixed age.