We present the color distributions of globular cluster ( GC ) systems for 100 Virgo cluster early-type galaxies observed in the ACS Virgo Cluster Survey , the deepest and most homogeneous survey of this kind to date .
While the color distributions of individual GC systems can show significant variations from one another , their general properties are consistent with continuous trends across galaxy luminosity , color , and stellar mass .
On average , galaxies at all luminosities in our study ( -22 < M _ { B } < -15 ) appear to have bimodal or asymmetric GC color distributions .
Almost all galaxies possess a component of metal-poor GCs , with the average fraction of metal-rich GCs ranging from 15 to 60 % .
The colors of both subpopulations correlate with host galaxy luminosity and color , with the red GCs having a steeper slope .
The steeper correlation seen in the mean color of the entire GC system is driven by the increasing fraction of metal-rich GCs for more luminous galaxies .

To convert color to metallicity , we also introduce a preliminary ( g – z ) - [ Fe/H ] relation calibrated to Galactic , M49 and M87 GCs .
This relation is nonlinear with a steeper slope for { [ Fe / H ] } \lesssim - 0.8 .
As a result , the metallicities of the metal-poor and metal-rich GCs vary similarly with respect to galaxy luminosity and stellar mass , with relations of { [ Fe / H ] } _ { MP } \propto L ^ { 0.16 \pm 0.04 } \propto M _ { \star } ^ { 0.17 \pm 0.04 } and { [ Fe / H ] } _ { MR } \propto L ^ { 0.26 \pm 0.03 } \propto M _ { \star } ^ { 0.22 \pm 0.03 } , respectively .
Although these relations are shallower than the mass-metallicity relation predicted by wind models and observed for dwarf galaxies , they are very similar to the mass-metallicity relation for star forming galaxies in the same mass range .
The offset between the two GC populations varies slowly ( \propto M _ { \star } ^ { 0.05 } ) and is approximately 1Â dex across three orders of magnitude in mass , suggesting a nearly universal amount of enrichment between the formation of the two populations of GCs .
We also find that although the metal-rich GCs show a larger dispersion in color , it is the metal-poor GCs that have an equal or larger dispersion in metallicity .
The similarity in the M _ { \star } – [ Fe/H ] relations for the two populations , implies that the conditions of GC formation for metal-poor and metal-rich GCs could not have been too different .
Like the color-magnitude relation , these relations derived from globular clusters present stringent constraints on the formation and evolution of early-type galaxies .