Wandzura-Wilczek relations allow us to access the color forces among quarks and gluons from off-forward scattering processes. I will present an analysis of the parton transverse momentum substructure of these processes involving Generalized Parton Distributions (GPDs). I will focus, in particular, on three helicity configurations that can be detected analyzing specific spin asymmetries: two correspond to longitudinal proton polarization and are associated with quark orbital angular momentum and spin-orbit correlations; the third, obtained for transverse proton polarization, is a generalization of the relation obeyed by the g2 structure function from inclusive polarized scattering. An additional relation connecting the off-forward extension of the Sivers function to an off-forward quark-gluon-quark term, known as the Qiu-Sterman term, will also be discussed.