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Two recent empirical developments in the study of extragalactic globularcluster (GC) populations are the color-magnitude relation of the blue GCs (the"blue tilt") and the nonlinearity of the dependence of optical GC colors onmetallicity. The color-magnitude relation, interpreted as a mass-metallicityrelation, is thought to be a consequence of self-enrichment. Nonlinearcolor-metallicity relations have been shown to produce bimodal colordistributions from unimodal metallicity distributions. We simulate GCpopulations including both a mass-metallicity scaling relation and nonlinearcolor-metallicity relations motivated by theory and observations. Depending onthe assumed range of metallicities and the width of the GC luminosity function(GCLF), we find that the simulated populations can have bimodal colordistributions with a "blue tilt" similar to observations, even though themetallicity distribution appears unimodal. The models that produce thesefeatures have the relatively high mean GC metallicities and nearly equal blueand red peaks characteristic of giant elliptical galaxies. The blue tilt isless apparent in the models with metallicities typical of dwarf ellipticals;the narrower GCLF in these galaxies has an even bigger effect in reducing thesignificance of their color-magnitude slopes. We critically examine theevidence for nonlinearity versus bimodal metallicities as explanations for thecharacteristic double-peaked color histograms of giant ellipticals and concludethat the question remains open. We discuss the prospects for furthertheoretical and observational progress in constraining the models presentedhere and for uncovering the true metallicity distributions of extragalacticglobular cluster systems.

The Mass-Metallicity Relation of Globular Clusters in the Context of Nonlinear Color-Metallicty Relations