  The two-flavor color superconductivity is studied over a wide range of baryon
density with a single model. We pay a special attention to the spatial-momentum
dependence of the gap and to the spatial-structure of Cooper pairs. At
extremely high baryon density (O(10^{10} rho_0) with rho_0 being the normal
nuclear matter density), our model becomes equivalent to the usual perturbative
QCD treatment and the gap is shown to have a sharp peak near the Fermi surface
due to the weak-coupling nature of QCD. On the other hand, the gap is a smooth
function of the momentum at lower densities (O(10 rho_0)) due to strong color
magnetic and electric interactions. To study the structural change of Cooper
pairs from high density to lower density, quark correlation in the color
superconductor is studied both in the momentum space and in the coordinate
space. The size of the Cooper pair is shown to become comparable to the
averaged inter-quark distance at low densities. Also, effects of the
momentum-dependent running coupling and the antiquark pairing, which are both
small at high density, are shown to be non-negligible at low densities. These
features are highly contrasted to the standard BCS superconductivity in metals.
