  We consider the class of gauges that interpolates between Landau- and
Coulomb-gauge QCD, and show the non-renormalisation of the two independent
ghost-gluon vertices. This implies the existence of two RG-invariant running
couplings, one of which is interpreted as an RG-invariant gauge parameter. We
also present the asymptotic infrared limit of solutions of the Dyson-Schwinger
equations in interpolating gauges. The infrared critical exponents of these
solutions as well as the resulting infrared fixed point of one of the couplings
are independent of the gauge parameter. This coupling also has a fixed point in
the Coulomb gauge limit and constitutes a second invariant charge besides the
well known colour-Coulomb potential.
