We present a method for deriving light-weighted stellar metallicities and ages from high-resolution galaxy spectra, based on the new population synthesis code of Bruzual & Charlot (2003). The method relies on the simultaneous fit of several optical spectral absorption features that are sensitive to either age or metallicity, but not to the $\alpha$-elements abundance ratio. We have constructed a library of stochastic star formation histories, which we have used to derive median-likelihood estimates of ages and metallicities for $\sim10^5$ galaxies extracted from the Sloan Digital Sky Survey Data Release One (SDSS DR1), spanning the full range in star formation activities, from dormant early type to actively star forming. Here we discuss the results for early-type galaxies. We show that the $g-r$, $M_r$ color-magnitude relation for these galaxies is driven primarily by changes in metallicity and in heavy-element abundance ratios. Changes in light-weighted age contribute mainly to the scatter about the relation. This is consistent with previous interpretations of this relation based on lower resolution models.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html