  We study the speed of sound in strong-interaction matter at zero temperature
and in density regimes which are expected to be governed by the presence of a
color-superconducting gap. At (very) high densities, our analysis indicates
that the speed of sound approaches its asymptotic value associated with the
non-interacting quark gas from below, in agreement with first-principles
studies which do not take the presence of a color-superconducting gap into
account. Towards lower densities, however, the presence of a gap induces an
increase of the speed of sound above its asymptotic value. Importantly, even if
gap-induced corrections to the pressure may appear small, we find that
derivatives of the gap with respect to the chemical potential can still be
sizeable and lead to a qualitative change of the density dependence of the
speed of sound. Taking into account constraints on the density dependence of
the speed of sound at low densities, our general considerations suggest the
existence of a maximum in the speed of sound. Interestingly, we also observe
that specific properties of the gap can be related to characteristic properties
of the speed of sound which are indirectly constrained by observations.
