HID's are what I'll cover for this entry. These "high intensity discharge" bulbs are often tagged as the signature of a "ricer" or someone who essentially knows nothing about vehicles but "tricks" them out. However, HID's do have a functional use as well, as if you get the right color temperature, they are brighter than standard halogen bulbs. In most cases however, DIY tuners don't really get them for reasons of practicality. Below is a chart on the temperatures and the colors they omit.
As you can see, the higher the temperature after 6k, there starts to get a blueish tint to the light. 30k is more purple than blue. There are other dfferences as well. The higher the temp on this chart after 6k, the less light is emitted. Also, there is the issue of legality. 10k is about as high as you can go without being pulled over every two seconds in most states, and in others even 8k is too much. These numbers and later are what these "ricer" drivers tend to aim for. This is not to say that these colors do not look good or are stupid; many show cars incorporate them. That is the difference, though. There is a specific, legal use for them then. Ricers don't understand that or don't care and do it anyway.
Often, when they decide to simply do it on a whim, they don't think about what is proper anyway. HID's do not belong in reflector housings, they should be placed in projector housings.
Why this really is significant is that most newer cars that have projector housings come stock with lower temp HID's installed, many times. Therefore, the cars being swapped have reflector. The effect of this? That rage in your soul when one drives past you at night, blinding you. A proper setup with the proper housings will not do this to you, or your eyes.
Bottom Line? If you are going to install HID lighting, do it for the right reasons then do it right.