Voyager and Galileo images of Europa show striking surface color variations, including a stark contrast between the leading and trailing hemispheres and a marked association with surface geology. Such patterns likely reflect the combined influences of endogenic geologic resurfacing and exogenic sulfur radiolysis on the surface composition. Using visible-wavelength spectra of the trailing hemisphere obtained with the Hubble Space Telescope, we investigate the compositional differences underlying these color variations and attempt to disentangle endogenous from exogenous influences. Our data are sensitive to the signatures of irradiation-produced color centers in both chloride and sulfate salts, as well as to the signatures of several sulfur allotropes. We map multiple spectral features across the trailing hemisphere and compare their distributions with the geographies of geologically young terrain, magnetospheric bombardment, and surface color. The spatial distributions of some spectral features suggest that they represent purely exogenous sulfur radiolysis products, while the geographies of others are better explained by radiolysis products formed from a mixture of endogenous material and Iogenic sulfur.