Hey Bob. It's a difficult project. First, you have the issue of the synthetic cloth of which the seating surfaces are made. Rayon, nylon and polyester are all very smooth surfaced polymers. Getting them to take color after they are made is almost impossible, the reason the colors are blended into the polymers at time of manufacture--or dyed with a special process that lends itself to bulk (see below). Stranded threads, thread made up of multiple filaments, take dye a little better, but only because the dye can bet caught, so to speak, between filaments. Still not much adhesion though. The folks who make Krylon Fusion paint can sure tell you how tough it is to bond coloring agents to polymers! Using natural dyes like Rit, will only give you color for a little while...but may color clothing undesirably.

Olefins are polymers woven together with natural fibers like cellulose to create a fabric that breathes more. These can be dyed more easily. A couple of years ago I tried to find out what type of thread Volvo's cloth seat covers are made from before embarking on a dyeing project. It would seem that seat faces would be a good place for a fabric that breathes, but I never found info. Personally I think they are rayon or polyester. If they are blended, that is with cotton threads, they may dye with natural dyes, but you will get a two tone effect as the tan threads won't take the dye.

To dye the synthetic cloth completely, you need what is called dispersion dye. This is a two part solution that includes a chemical which softens the surface of the polymer strands so a chemical bonding can take place (simplified explanation of the bonding process). It's nasty, dangerous stuff and messy. The other processes involve heating the cloth. While safer as far as chemicals, unfortunately the temp required is hotter than you can get by just boiling the cloth in a pot of water. I think on the order of 350 degrees--can't remember. For the dispersion dye, Google "dyeing synthetic fabric with dispersion dye", there are lots of articles on how to.

I don't know if the dispersion agent will affect the vinyl, and if it does, how evenly any color would take. You would probably have to go back afterwards, mask off all the cloth at the welting and use one of the upholstery sprays that are available. They've gotten very good! Vinyl is PVC, not the same type of polymer as rayon and polyester and such. Testing is the key. You can buy dispersion dyes on line, quantity being the only question.

Good luck...
Dave