Is there a way to restore the color on my black seatbelt webbing?

I have heard of people using store bought dye (can't remember the brand name). However, if your belts have faded, they may need to be replaced. Sunlight reduces the strength of the material the belts are made of.

If the webbing is in really good condition, buy some RIT dye at the grocery store, mix it up in a bucket or something your wife won't kill you for using, and drop the belts in there. Then I would rinse real well and hang to dry. They will come out looking great. If the webbing is frayed or worn, it would be best to get them re-webbed. It's expensive, but so is being disabled.

RIT, that's it. I couldn't remember.

I highly recommend replacing the original webbing. Are you willing to trust your life to 30 year old seat belts? I wasn't.