Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

Stitching I can't help with, but if you're looking for an exacting museum-quality color match, a person could but a white cord and painstakingly brush paint it appropriately.  I'd experiment first as you don't want something that will crack and flake from bending.  Perhaps food coloring would work, as it soaks in. 

Another possibility is to purchase a paint additive with a "flexant" component.  My brother mixed it with spray lacquer and used it successfully to paint the vinyl seat in an old Chevy pickup.  I used it for similar purposes.  These flexant components were sold at auto parts stores for when body men had to paint the flexible plastic insert that goes between the old 5-mph crash bumpers and the body of the car.  Think 80's Ford Escort. 

Again, you'd have to experiment, but some possibilities for you to consider.

Paul