  The leading-order accurate description of top quark pair production, as
usually employed in standard Monte Carlo event generators, gives no rise to the
generation of a forward--backward asymmetry. Yet, non-negligible --
differential as well as inclusive -- asymmetries may be produced if coherent
parton showering is used in the hadroproduction of top quark pairs. In this
contribution we summarize the outcome of our study of this effect. We present a
short comparison of different parton shower implementations and briefly comment
on the phenomenology of the colour coherence effect at the Tevatron.
