  The far-ultraviolet (UV) counts and the deep optical spectroscopic surveys
have revealed an unexpected number of very blue galaxies (vBG). Using
constraints from the UV and optical, we apply the galaxy evolution model PEGASE
(Fioc & Rocca-Volmerange 1997, hereafter FRV) to describe this population with
a cycling star formation. When added to normally evolving galaxy populations,
vBG are able to reproduce UV number counts and color distributions as well as
deep optical redshift distributions fairly well. Good agreement is also
obtained with optical counts (including the Hubble Deep Field). The number of
vBG is only a small fraction of the number of normal galaxies, even at faintest
magnitudes. In our modelling, the latter explain the bulk of the excess of
faint blue galaxies in an open Universe. The problem of the blue excess remains
in a flat Universe without cosmological constant.
