  In this paper we discuss the mix of star-forming and passive galaxies up to
z~2, based on the first epoch VIMOS-VLT Deep Survey (VVDS) data.In agreement
with previous works we find that the galaxy rest-frame color distribution
follows a bimodal distribution at z<=1, and we establish that this bimodality
holds up to z~2. The details of the rest-frame color distribution depend
however on redshift and on galaxy luminosity: faint galaxies are bluer than the
luminous ones over the whole redshift range of our data, and galaxies become
bluer as redshift increases. This blueing trend does not depend, to a first
approximation, on galaxy luminosity. Using our spectroscopic dataset we can
also separate galaxies based on a star-formation, estimated combining the
equivalent width of the [OII] emission line and the strength of the Dn(4000)
break. The comparison between this spectral classification and the rest-frame
colors shows that about 35-40 % of the red objects are star forming galaxies.
Hence we conclude that the red sequence cannot be used to effectively isolate a
sample of purely passively evolving objects within a cosmological survey. We
also find that the color-magnitude relations derived for the color and for the
spectroscopically selected early-type galaxies have remarkably similar
properties, with the contaminating star-forming galaxies within the red
sequence objects introducing no significant offset in the rest frame colors.
Therefore the average color of the red objects does not appear to be a very
sensitive indicator for measuring the evolution of the early-type galaxy
population.Finally, we use the multi-band VVDS photometric data and SED fitting
to derive multi-color galaxy types, which have a slightly higher efficiency
than rest-frame color in isolating the passive, non star-forming galaxies
within the VVDS sample.
