  In QCD hard scattering cross sections, the color content of the underlying
hard scattering evolves with a factorization scale. This evolution is
controlled by an anomalous dimension matrix, specific to each hard-scattering
reaction. Anomalous dimensions are determined from the renormalization of
products of ordered exponentials of the gauge field, which describe the
coherent radiation of gluons by incoming hadrons and the observed jets or
particles of the final state. The anomalous dimensions depend on the kinematics
of the underlying hard scattering, but are free of collinear singularities. A
number of these matrices are available in the literature. Here, we exhibit
one-loop mixing matrices for the full list of $2 \to 2$ reactions involving
light quarks and gluons. The eight-by-eight anomalous dimension matrix for
gluon-gluon scattering shows a simplified structure in the basis corresponding
to definite color exchange in the $t$-channel.
