  We review recent progress of understanding and resolving instabilities driven
by mismatch between the Fermi surfaces of the pairing quarks in 2-flavor color
superconductor. With the increase of mismatch, the 2SC phase exhibits
chromomagnetic instability as well as color neutral baryon current instability.
We describe the 2SC phase in the nonlinear realization framework, and show that
each instability indicates the spontaneous generation of the corresponding
pseudo Nambu-Golstone current. The Nambu-Goldstone currents generation state
covers the gluon phase as well as the one-plane wave LOFF state. We further
point out that, when charge neutrality condition is required, there exists a
narrow unstable LOFF (Us-LOFF) window, where not only off-diagonal gluons but
the diagonal 8-th gluon cannot avoid the magnetic instability. In this Us-LOFF
window, the diagonal magnetic instability cannot be cured by off-diagonal gluon
condensate in the color superconducting phase.
