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We present the first multi-color view of the scattered light disk of theHerbig Ae star HD 163296, based on coronagraphic observations from the HubbleSpace Telescope Advanced Camera for Surveys (ACS). Radial profile fits of thesurface brightness along the disk's semi-major axis indicates that the disk isnot continuously flared, and extends to 540 AU. The disk's color (V-I)=1.1 at aradial distance of 3.5 arcseconds is redder than the observed stellar color(V-I)=0.15. This red disk color might be indicative of either an evolution inthe grain size distribution (i.e. grain growth) and/or composition, both ofwhich would be consistent with the observed non-flared geometry of the outerdisk. We also identify a single ansa morphological structure in our F435W ACSdata, which is absent from earlier epoch F606W and F814W ACS data, butcorresponds to one of the two ansa observed in archival HST STIS coronagraphicdata.  Following transformation to similar band-passes, we find that the scatteredlight disk of HD 163296 is 1 mag arcsec$^{-2}$ fainter at 3.5 arcseconds in theSTIS data than in the ACS data. Moreover, variations are seen in (i) thevisibility of the ansa(e) structures, in (ii) the relative surface brightnessof the ansa(e) structures, and in (iii) the (known) intrinsic polarization ofthe system. These results indicate that the scattered light from the HD 163296disk is variable. We speculate that the inner disk wall, which Sitko et al.suggests has a variable scale height as diagnosed by near-IR SED variability,induces variable self-shadowing of the outer disk. We further speculate thatthe observed surface brightness variability of the ansa(e) structures mayindicate that the inner disk wall is azimuthally asymmetric.

The HD 163296 Circumstellar Disk in Scattered Light: Evidence of Time-Variable Self-Shadowing