The guitar hero 3 guitars are all white & don't have a slide bar (sp?). They work fine though, I'm using 2 at the moment. No need to pay exorbitant prices for a paint job.
It's a little touch-sensitive bar that you can use at certain places (usually solos where you have notes connected by strings), or to "rub" to give a wah-wah effect. Lets you get extra star power if you do the rub during star power phrases.