  We derive the spatial and wavelength behavior of dust attenuation in the
multiple-armed spiral galaxy VV191b using backlighting by the superimposed
elliptical system VV191a in a pair with an exceptionally favorable geometry for
this measurement. Imaging using JWST and HST spans the wavelength range 0.3-4.5
microns with high angular resolution, tracing the dust in detail from 0.6 to
1.5 microns. Distinct dust lanes continue well beyond the bright spiral arms,
and trace a complex web, with a very sharp radial cutoff near 1.7 Petrosian
radii. We present attenuation profiles and coverage statistics in each band at
radii 14-21 kpc. We derive the attenuation law with wavelength; the data both
within and between the dust lanes clearly favor a stronger reddening behavior
(R ~ 2.0 between 0.6 and 0.9 microns, approaching unity by 1.5 microns) than
found for starbursts and star-forming regions of galaxies. Power-law extinction
behavior lambda^(-beta) gives beta=2.1 from 0.6-0.9 microns. R decreases at
increasing wavelengths (R~1.1 between 0.9 and 1.5 microns), while beta steepens
to 2.5. Mixing regions of different column density flattens the wavelength
behavior, so these results suggest a different grain population than in our
vicinity. The NIRCam images reveal a lens arc and counterimage from a
background galaxy at z~1, spanning 90 degrees azimuthally at 2.8" from the
foreground elliptical galaxy nucleus, and an additional weakly-lensed galaxy.
The lens model and imaging data give a mass/light ratio 7.6 in solar units
within the Einstein radius 2.0 kpc.
