Weird. The 2000/2001 models had a "dusk" interior color which was a slightly bluish grey, and 2002+ have a plain grey that is a little lighter. Otherwise, there has been the Sage (khaki-like) color and the charcoal (black) but that's it. Anything else would have been aftermarket. For 2003 there have been some factory "rugged leather" versions, I've seen just one myself.
Lots of dealers a couple of years ago were offering "extreme edition" Xterras with aftermarket leather seats and interior trim with the Xterra logo stitched in the seats. I've never ever heard of anyone doing vinyl seats on an X.

Brent
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