The welting is available from
Embossed Welt Seat Cord or
Trim Bright Accents. It's a simple press-in fit, though I had to super-glue the ends on the door panels under the window trim. The stuff is hollow, so if you have to butt the ends together (like around the shifter) you just use a cut-off drywall nail as a connector. Mr. Mike's (Trim Bright) is more expensive, but has a yellow if you want - actually, it's more of an orange/yellow.
I also did my airbag and A pillers, and am going to do the dash surround and the side covers on the seats.
Thanks for the props!