  The spectrum of meson and diquark excitations in cold color-superconducting
(2SC) quark matter is investigated under local color and electric neutrality
constraints with $\beta$-equilibrium. A 2-flavored Nambu--Jona-Lasinio type
model including a baryon $\mu_B$, color $\mu_8$, and electric $\mu_Q$ chemical
potentials is used. Two relations between coupling constants $H$ and $G$ in the
diquark- and quark-antiquark channels, correspondingly, are treated, $H=3G/4$
and $H=G$. At $H=3G/4$ the gapless- and at $H=G$ the gapped neutral color
superconductivity is realized. It is shown that color and electrical neutrality
together with $\beta$-equilibrium lead to a strong mass splitting within the
pion isotriplet in the 2SC phase (both gapped and gapless), in contrast with
non--neutral matter. It is also shown that the properties of the physical
$SU(2)_c$-singlet diquark excitation in the 2SC ground state varies for
different parameterization schemes. Thus, for $H=3G/4$ one finds a heavy
resonance with mass $\sim$ 1100 MeV in the non--neutral (gapped) case, whereas,
if neutrality is imposed, a stable diquark with mass $\sim\mu_Q\sim$ 200 MeV
appears in the gapless 2SC phase. For $H=G$, there is again a resonance (with
the mass $\sim$ 300 MeV) in the neutral gapped 2SC phase. Hence, the existence
of the stable massive SU(2)$_c$-singlet diquark excitation is a new peculiarity
of the gapless 2SC.
