I always thought the silver colour specific to nerves was due to the myelin sheaths, but I've observed that unmyelinated C fibres display that same silvery appearance. Where does this colour come from? And can you distinguish myelinated from unmyelinated fibre bundles with the naked eye from their colour?
I think the whitish color is due to the outer layer of nerve bundles: the epineurium. This surrounds all nerves, whether they contain myelinated fibers, unmyelinated fibers, or both.
Nerves are bundles of axons (Fig. 1). Whether the axons are myelinated or not, the gross anatomy is similar; axons within a nerve are bundled into fascicles and surrounded by perineurium. Those fascicles are again bundled up and surrounded by epineurium. It is this epineurium that you probably are seeing and it has a whitish appearance (Fig. 2).
The surface of a nerve therefore does not contain myelin; myelin is present around individual axons and is not exposed. Hence, whether a nerve contains myelinated axons, unmyelinated ones, or both will not determine its outward appearance.
Fig. 1. Anatomy of a nerve bundle. source: EasyNoteCards
Macroscopic view of a nerve targeted for epineurial repair. source: wikipedia