What Merlin said. If you leave the yellow tint on the lamps, then were to drop in a HID kit of 8000K+, you will make green light. Not to mention the fact that those color temp lights have only a FRACTION of the lumens the stock halogen bulbs have.
I need to go copy my post about HIDs and paste it here.
On the topic of Retrofit's, im really starting to dig what these guys have to offer.