[trottida]

I'm thinking that is grey. Regardless it is from a 96 and I believe the buckle changed in 99 and there may have been a colour change too.

The part number you are looking for is 21304496. The colour is Medium Biscuit II and it was used in 1999 through 2002 sedans. I see that it is still available at a few dealerships in the states. Here is a link to the GM part

BELT KIT,R/SEAT (RETR SI)(MD BISC II) - RH.

PartsVoice indicates this dealer has one >> http://www.friesenchevy.com/

This site looks to have one too >> https://www.tascaparts.com/vintage-g...si-m-21304496/

As does this one >> https://www.wholesalegmpartsonline.c.../21304496.html

You can also plug that part number into eBay and get a few more hits. The part number is on the tag sewn to the part itself.