HID lights is what you would see on your more expensive cars but not others are getting them. Most that you see that are from the factory are 6000k. The higher the K the darker the color.
Make sure you buy a good kit and I wouldnt get anything higher then 6k because they are a nice white light and if you go to blue they suck in the rain.
I had them on my dodge ram for almost 2 yrs before they started giving me troubles(ballast) It was the best kit I could get but none of them are trouble free it seems like. As nice as they were I pulled them out and installed PIAA's
I have projector Head lights on my Denali and put a HID kit of 6000k. They are as bright as 100w bulbs but are only 35watts. The install tells you they are much brighter than you halagen lights and you should adjust the light beam down to help on comming traffic. 6000k is as high as I would go. It is the pure white light and is really much better seeing in all weather conditions. I have HID in the fog lights also. However those are 8000K and are a light, light blue in color. Big difference. Stay with the 6000K.