  We use 2-color QCD as a model to study the effects of simultaneous presence
of the so-called $\theta$ parameter, chemical potentials for baryon number,
$\mu_B$ and for isospin charge, $\mu_I$. We pay special attention to $\theta$,
$\mu_B$, $\mu_I$ dependence of different vacuum condensates, including chiral
and diquark condensates, as well as the gluon condensate, $<G^2>$, and the
topological susceptibility. We find that two phase transitions of the second
order will occur when $\theta$ relaxes from $\theta=2\pi$ to $\theta=0$, if
$\mu$ is of order of the pion mass. We demonstrate that the transition to the
superfluid phase at $\theta = \pi$ occurs at a much lower chemical potential
than at $\theta = 0$. We also show that the strong $\theta$ dependence present
near $\theta = \pi$ in vacuum (Dashen's phenomenon), becomes smoothed out in
the superfluid phase. Finally, we comment on the relevance of this study for
the real world with N_c=3.
