Yep, the patina from the etching goes away with usage and fades with age - well, the difference fades. So, a spa treatment could be good for the looks.

Hamon: technically, it's not hamon. Hamon is the visual effect when mono-steel is differentially hardened - so when you dip it in some kind of acid it etches differently.

What you have is a sanmai construction - the principle is the same - harder steel resist the etch more so there's a difference in colour - but it's actually two different steels.

This is hamon:

Edit: wax - that's OK -anything that keeps the blade from direct exposure to the environment.