Werd.
The original grease that you install them with WILL wear out over time, creating sticktion(friction) in the bushing, a resistance to movement and causing the bushings to wear. OP, if you look in my thread (Project: Do Work) I installed grease nipples at all the poly bushings, I think I posted the How-to link in the thread somewhere as well.
Edit:
How do you figure? According to ES you dont need to regrease them, yes. But ideally you want as close to zero friction as possible in your suspension components and a well greased bushing will get you a hell of alot closer to that then a dry piece of poly and metal rotating together. That said, NO its not imperitave that you ever regrease them once you put them in, but performance/longevity wise it is a good idea.
Good to know about the red/black thing though, didnt know that.