i don't think that works i went on the RIT website and it says it doesn't work on rubber:
this is from the website ...
..but there are fabrics that will not accept dye such as...
- Fabrics with 50% or more polyester content
- 100% acrylic, fiberglass, or metallic fibers
- Fabrics with rubber backing (bath mats or throw rugs)
- Fabrics with special finishes such as water repellents
- Fabrics with bleach damage or extensive staining
- Fabrics washable only in cold water or labeled "dry clean only"