The difference between the N80 and F80 is....nothing, they were just different designations for the America market (N) and the rest of the world (F).
But yes, the N80/F80 did come in both silver and black finishes and I think the reason is this, it was an amateur camera and the silver would hold up much better than if it was applied to a semi-pro/pro camera like the F100. It's remarkable how ugly a silver camera quickly becomes when it gets scratches caused by hard use through to the black plastic, so the F100 was never sold with an option for silver, which is not to say Nikon don't have one in a cupboard.