  Light emission in the first hours and days following core-collapse supernovae
(SNe) is dominated by the escape of photons from the expanding shock heated
envelope. In a preceding paper, Paper I, we provided a simple analytic
description of the time dependent luminosity, $L$, and color temperature,
$T_{\rm col}$, valid up to H recombination ($T\approx0.7$ eV), for explosions
of red supergiants with convective polytropic envelopes without significant
circum-stellar medium (CSM). The analytic description was calibrated against
"gray" (frequency-independent) photon diffusion numeric calculations. Here we
present the results of a large set of 1D multi-group (frequency-dependent)
calculations, for a wide range of progenitor parameters (mass, radius,
core/envelope mass ratios, metalicity) and explosion energies, using opacity
tables that we constructed (and made publicly available), including the
contributions of bound-bound and bound-free transitions. We provide an analytic
description of the small, $\simeq10\%$ deviations of the spectrum from
blackbody at low frequencies, $h\nu< 3T_{\rm col}$, and an improved (over Paper
I) description of `line dampening' for $h\nu> 3T_{\rm col}$. We show that the
effects of deviations from initial polytropic density distribution are small,
and so are the effects of `expansion opacity' and deviations from LTE
ionization and excitation (within our model assumptions). A recent study of a
large set of type II SN observations finds that our model accounts well for the
early multi-band data of more than 50\% of observed SNe (the others are likely
affected by thick CSM), enabling the inference of progenitor properties,
explosion velocity, and relative extinction.
