  We perform an statistical analysis of galaxies in pairs in a Lambda-CDM
scenario by using the chemical GADGET-2 of Scannapieco et al. (2005) in order
to study the effects of galaxy interactions on colours and metallicities. We
find that galaxy-galaxy interactions can produce a bimodal colour distribution
with galaxies with significant recent star formation activity contributing
mainly to blue colours. In the simulations, the colours and the fractions of
recently formed stars of galaxies in pairs depend on environment more strongly
than those of galaxies without a close companion, suggesting that interactions
play an important role in galaxy evolution. If the metallicity of the stellar
populations is used as the chemical indicator, we find that the simulated
galaxies determine luminosity-metallicity and stellar mass-metallicity
relations which do not depend on the presence of a close companion. However, in
the case of the luminosity-metallicity relation, at a given level of
enrichment, we detect a systematic displacement of the relation to brighter
magnitudes for active star forming systems. Regardless of relative distance and
current level of star formation activity, galaxies in pairs have stellar
populations with higher level of enrichment than galaxies without a close
companion. In the case of the gas component, this is no longer valid for
galaxies in pairs with passive star formation which only show an excess of
metals for very close pair members, consequence of an important recent past
star formation activity. (Abridged).
