Straw color
 

Does the straw color deteriorate over time? Or with use?
If a part is white, does it mean that it has been altered?

Yes.
Yes - it rubs off, it's very thin layer. Supposedly sunlight fades it too.
Not necessarily. It probably means it's been rubbed, scrubbed, and polished a lot, but it could be a not original part. Would have to see photos.