The purple band is the stock antenna that comes with the G4/G5 for the 700-800 band. For the G5, the VHF/UHF antenna is internal.
I think the green tip is for one of the international models that does not have the 700-800 band. The order options there for the G4 single or G5 dual band allows you to have a pager with just VHF or UHF.
There are a couple of threads on different antennae you can buy from other manufacturers. Motorola make a couple that have gotten some good reviews.
Thanks guys for the information. I couldn't find anything about the antenna other than the picture on the website. I'm not having any problems with my g4 but always looking for something to make it a little bit better lol thanks��