Spot on Dunk.
All OEM Xenons come with 4300k bulbs, so they are the same light colour.
The reason some look different colours is down to the alignment of the projector beam.
There's a bluish tint caused by refraction of the lens at the top of the beam - and that's what the aftermarket bulb kits are trying to emulate by using higher k-rating HID bulbs in normal reflectors.
If I look at my own car - with matching OEM bulbs & headlights - you can see slightly different colours between the two headlights depending on where you stand in front - because of the angle that you're looking at the beam.
The other cause of different colours in Mercs is that there are two sorts of Xenon headlights, the normal "projector" types (using a D2S type bulb) that Audi's use, but also a special D2R bulb for fitting into Xenon reflector headlights (which Merc use).
The differences between the reflector and projector beams will present different appearances - but all OEM bulbs of both D2S and D2R type are 4300k colour...
Its only the aftermarket kits that use different colours of bulbs to emulate the blue prism tint of an OEM headlight, but the actual light output reduces as the colour K number increases.
4300k bulbs put most lumens out. 6000k are a bit less bright but anything above 6000k colour has a much lower lumen output.