  Color superconductivity of QCD at finite density, temperature and flavor
asymmetry is studied within an approximation which the interaction is modeled
upon four--fermion interactions. We calculate the thermodynamic potential in
the so-called NJL-type model and study the phase structure at finite density,
temperature and flavor asymmetry. We find that a mixed phase appears at
sufficiently large flavor asymmetry and low temperature. A tricritical point in
the $T$-$\mu_B$-$\mu_I$ plane is also found.
