Be careful with what you buy. To get the really nifty colors, you'll need a true HID kit (High Intensity Discharge). These bulb systems run much hotter than normal halogen/xenon lights... therefore giving off the colored effect. But you need a special ballast, new wires and sometimes a new bulb housing.
You can get a lot whiter light by just switching out your lights. But be prepared to lose brightness and don't get any bulb thats rated higher than your factory harness. If you have a normal 55/65 watt harness, putting a 100 watt bulb in will make it super bright... before frying the wires after a short while.
I put some Optilux headlights in my Saab projectors and they look whiter then stock... but they aren't so tinted that I lose visability. I put some REALLY blue lights in my last Jeep and they absolutely sucked for light output.