We study an O(N) scalar model under shear flow and its Nambu-Goldstone modes associated with spontaneous symmetry breaking O(N)→O(N-1). We find that the Nambu-Goldstone mode splits into an infinite number of gapless modes, which we call the rainbow Nambu-Goldstone modes. They have different group velocities and the fractional dispersion relation ω∼k_{1}^{2/3}, where k_{1} is the wave number along the flow. Such behaviors do not have counterparts in an equilibrium state.