On The Origin of the Blue Tilt in Extragalactic Globular Cluster Systems
  Some early-type galaxies show a correlation between color and integrated magnitude among the brighter metal-poor globular clusters (GCs). This phenomenon, known as the blue tilt, implies a mass-metallicity relationship among these clusters. In this paper we show that self-enrichment in GCs can explain several aspects of the blue tilt, and discuss predictions of this scenario. 
Jay Strader (CfA), Graeme Smith (UCO/Lick)