I believe the silver keys ended with the 2008 model. Here's what my 2009 Unibody keyboard looks like. Depending on where the light hits, it's either new looking or very shiny.
I think these keys collected oil just as fast, but they just didn't look as shiny because the finish was more forgiving.
View attachment 2354750
I just took out my 2007 (my 2008 17 died in 2018) and it looks fine. The silver is already shiny so skin oils don't look any different from the keys.