  The bulk viscosities of two color-superconducting phases, the color-flavor
locked (CFL) phase and the 2SC phase, are computed and compared to the result
for unpaired quark matter. In the case of the CFL phase, processes involving
kaons and the superfluid mode give the largest contribution to the bulk
viscosity since all fermionic modes are gapped. In the case of the 2SC phase,
ungapped fermionic modes are present and the process u+d <-> u+s provides the
dominant contribution. In both cases, the bulk viscosity can become larger than
that of the unpaired phase for sufficiently large temperatures (T >~ 1 MeV for
CFL, T >~ 0.1 MeV for 2SC). Bulk viscosity (as well as shear viscosity) is
important for the damping of r-modes in compact stars and thus can potentially
be used as an indirect signal for the presence or absence of
color-superconducting quark matter.

Nuclear Theory;Astrophysics;High Energy Physics - Phenomenology