http://faq.auto.light.tripod.com/hl-hid-bulbs.htm
http://faq.auto.light.tripod.c...t.doc
These are just some interesting articles I found.
As far as the types of HID, automotive applications use Metal Halide HID's because of their quick start-up times. The other types takes up to several minutes before they can produce any effective lighting.
To make an effective yellow HID light, I might consider the use of a Dichroic filter. A yellow pass filter would work well here. Dichroic filters are different than tinted lenses in that instead of tinting the colors, it just traps a certain range of colors of light. In the case of a yellow pass, it essentially just traps the blue light in. This is the same way some of the halogen aftermarket fog lights make fore such bright yellow colors(PIAA, CATZ). Depending on what they coat with the filter(lens or bulb) you'll notice a bluish irridium color. You see blue in this instance as the blue light that hits it from the outside is being reflected back at you. This is probably the most efficient way to get a yellow HID look and has the fewest drawbacks. But I'm not automotive lighting expert, so I am not sure what other problems, if any, this might have.