  We discuss the Meissner effect for a color superconductor formed by cold
dense quark matter. Though color and ordinary electromagnetism are broken in a
color superconductor, there is a linear combination of the photon and a gluon
that remains massless. Consequently, a color superconducting region may be
penetrated by an external magnetic field. We show that at most a small fraction
of the magnetic field is expelled, and if the screening distance is the
smallest length scale in the problem there is no expulsion at all. We calculate
the behavior of the magnetic field for a spherical geometry relevant for
compact stars. If a neutron star contains a quark matter core, this core is a
color superconductor. Our results demonstrate that such cores admit magnetic
fields without restricting them to quantized flux tubes. Such magnetic fields
within color superconducting neutron star cores are stable on time scales
longer than the age of the universe, even if the spin period of the neutron
star is changing.
