> the PRIMA device provides only black-and-white vision

The Phosphenes[0] patients sense will depend on what is left of the retina. People using earlier systems reported some interpolation happened. Maybe that is true of this device too.

[0] - that is the name for the image the brain manifests in response to signals received by the visual cortex. Most of us experience them when we close our eyes and rub them, or maybe just see stuff that is unreal.