  We investigate the positivity of double parton distributions with a
non-trivial dependence on the parton colour. It turns out that positivity is
not preserved by leading-order evolution from lower to higher scales, in
contrast to the case in which parton colour is summed over. We also study the
positivity properties of the distributions at small distance between the two
partons, where they can be computed in terms of perturbative splitting kernels
and ordinary parton densities.
