Factory Mark VIIIs are 4300k.
+1
That's what I've always said/thought based on how they compared to KNOWN color temps I'd seen them compared to (in person, not in pics). For example, when I would pull my '72 Mark IV or Jaguar (I've put aftermarket 8000k HID's in both) up next to my parents' LSC at night, the 8000k's are ALOT more blue, and even make the LSC lights look a little yellow, almost like halogen headlights, when compared directly. 6000k also has more of a blue tint to it. Of course, years ago, I was told I was wrong and that the factory HID's were around 6000k, and that they only look more yellow/white in comparison because they're "old and worn out". I don't really buy this so much, but it's what I was told once. I still would say somewhere in the 4300 range if I had to guess.