  In a color superconductor the diquark condensates break spontaneously both
the color and ordinary electromagnetism, leaving a remanining rotated U(1)
symmetry unbroken. The gauge interactions associated to this rotated symmetry
may be considered as the in-medium electromagnetism. We compute the in-medium
photon self-energy in the presence of diquark condensates at high baryonic
density and weak coupling. This is done to one-loop order for the cases of two
and three quark flavors. For vanishing temperature, a detailed discussion is
given of the low momentum behavior of the photon polarization tensor. A simple
physical picture for the propagation of light in color superconducting media is
obtained. The main new effect is due to the diquark condensates, which lead to
a strong dielectric constant of the medium. The magnetic permeability remains
unchanged, because the primary condensates have vanishing spin and angular
momentum. In the two flavor case, an additional contribution arises due to
gapless quarks and electrons, which is responsible for Debye screening effects.
We also discuss the low energy effective theory for the three flavor case in
the presence of electromagnetic interactions.
