We report Hubble Space Telescope observations of six gravitational lenses with the Advanced Camera for Surveys. We measured the flux ratios between the lensed images in seven filters from 8140 Å to 2200 Å. In three of the systems, HE0512-3329, B1600+434, and H1413+117, we were able to construct UV extinction curves partially overlapping the 2175 Å feature and characterize the properties of the dust relative to the Galaxy and the Magellanic Clouds. In HE1104-1804, we detect chromatic microlensing and use it to study the physical properties of the quasar accretion disk. For a Gaussian model of the disk exp (- r 2/2r 2 s ), scaling with wavelength as rs vpropλ p , we estimate rs (λ3363) = 4+4 - 2 (7 ± 4) light days and p = 1.1 ± 0.6 (1.0 ± 0.6) for a logarithmic (linear) prior on rs . The remaining two systems, FBQ0951+2635 and SBS1520+530, yielded no useful estimates of extinction or chromatic microlensing. Based on observations made with the NASA/ESA Hubble Space Telescope. The Space Telescope Science Institute is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.