I'm sure everyones seen fretboards that have been discolored, and I've always wondered what could cause this. A couple examples, for those who aren't sure exactly what I'm talking about, are Eddie Van Halens Frankenstrat (http://www.vintagekramer.com/rare/stripes.jpg) and Fender sells "Road Worn" guitars (http://guitars.musiciansfriend.com/product/Fender-Road-Worn-50s-Stratocaster-Electric-Guitar?sku=526797) that are supposed to look beat up.

What causes this discoloration naturally? A local guitar store owner has his own guitars on display in his shop and some of the fretboards look like that, and I asked him what causes it. He went into a rant about how "some people baby their guitars, I play mine" which wasn't specifically what I was looking for.

Sweat? Simple wear on the fretboard? Anybody know?
Usage.Nothing more.Nothing less.

The following statement is true. The proceeding statement is false.
Oils from your fingers collect dirt on the fretboard and also will eventually wear through the finish on maple boards. The oil alone doesn't do it, but it's an important part. Otherwise it's just wear from using it.
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You know how when you change your strings they have loadsa crap on them?
How often o you change your neck?
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