Any way to do this ? I know you can change the wireframe, but the shaded color seems to fixed to grey.

You can append a Color SOP to the geometry instead if you want to do it on a per-object basis.

No clever way to do it at the OBJ level or even better at the Network Box level ?

Other than assigning a material at the object level with the desired color, no.

Ok, thanks for clearing that up.

may it happen you're looking for D > Material > Default Material

isamarsh
No clever way to do it at the OBJ level or even better at the Network Box level ?

Actually yes. Parameter Pane -> Options (gear icon) -> Add Visiualizer.

Then add a constant or random color at detail level.