Metal-rich and metal-poor globular clusters in ellipticals: Did we learn anything? or Constraints on galaxy formation and evolution from globular cluster sub-populations

A brief review on globular cluster sub-populations in galaxies, and their constraints on galaxy formation and evolution is given. The metal-poor and metal-rich sub-populations are put in a historical context, and their properties, as known to date, are summarized. We review why the study of these sub-populations is extremely useful for the study of galaxy formation and evolution, but highlight a few caveats with the current interpretations. We re-visit the current globular cluster system formation scenarios and show how they boil down to a single scenario for the metal-poor clusters (namely the formation in ``universal'', small fragments at high $z$) and that a hierarchical formation seems favored for the metal-rich clusters.