seat belt colors

[Diablo]

i have a 91 Daytona Shelby and i decided i didn't like the stock gray interior on so i am changing the color. i have all of the back panels painted black and will be doing the dash and door panels as soon as i can get more paint. my problem is the seatbelt straps are still gray. my brother tried using some of the vinyl die he got at the automotive store but that left his seat belts too stiff to go through the retraction mechanism. i don't know what would work to turn them black. has anyone ever successfully changed the color of their seat belt straps without making them hard and crusty if so what did you use?

thanks