The other thread mentions dying white with RIT dye. I remember using this to dye white nylon parts when I was racing R/C cars, however even the website says it won't work on rubber:
http://www.ritdye.com/dyeing-techniques/tips-success
a few forums say it does work, but I would wonder how long it would last (and is the dye going to transfer to the ball, and then transfer that color to other parts of the playfield?) Not sure I would try this, at least not on a nice pinball.