  We study the instabilities of quark matter in the framework of a generalized
Nambu--Jona-Lasinio model, in order to explore possible competition between
three-quark clustering to form nucleons and diquark formation leading to color
superconductivity. Nucleon and $\Delta$ solutions are obtained for the
relativistic Faddeev equation at finite density and their binding energies are
compared with those for the scalar and axial-vector diquarks found from the
Bethe-Salpeter equation. In a model with interactions in both scalar and axial
diquark channels, bound nucleons exist up to nuclear matter density. However,
except at densities below about a quarter of that of nuclear matter, we find
that scalar diquark formation is energetically favored. This raises the
question of whether a realistic phase diagram of baryonic matter can be
obtained from any model which does not incorporate color confinement.
