Color Transparency and Color Opacity in Coherent Production of Vector Mesons off Light Nuclei at small x

Coherent electroproduction of vector mesons off $^2$H and $^4$He is considered in the kinematics of deep inelastic scattering. Special emphasis is given to the $-t\sim 0.8-1$ GeV$^2$ region where the cross section is dominated by the interaction of the $q\bar q$ configuration in the $\gamma^*$ with two nucleons. These kinematics provide the unique possibilities to study quantitatively in vector meson production the onset of Color Transparency with increasing $Q^2$ as well as its gradual disappearance at very small $x$, i.e., perturbative Color Opacity.