the 5000k range is almost pure white

 

Common mistake here. 6000k is a study in contradiction.

The light color is bluer (well beyond whiteness below 5000k but have less output (partly due to the color temperature).

You need more power (wattage) to actually improve output.

 

Hmm, are you sure they are firing up? HIDs will have a ignite period of color change but they shouldn't look yellow. The only thing that ever looked yellow to me was the DRL (high beam at partial power) which may have caused you to think the halogen was actually the low beam

 

Got pictures of the lights on?

 

This a good point, but unless OP has a Canadian model, it should not be equipped with DRLs making the high beams operate at 50% to serve as DRLs.

As far as the previous picture of the two bulbs side-by-side, it also looks like your HID bulb is already a D2S bulb which is not OEM spec for an '05. The main difference between the D2S and the D2R is that the D2R has some metal shielding covering part of the glass like the picture below and the pole should not be blue.



I would guess that the previous owner already swapped in some D2S bulbs which were not very good quality which is causing them to fade in color or not operate at full brightness.

It sounds like you already made your purchase, so it's too late, but just to belabor the point regarding color temperature, going higher up in the color spectrum does not increase output or usable light. 5000K-5500K is really the highest you should go in order to get that "white light look" while compromising function. The reason for this comes down to the anatomy and photoreceptors of the human eye which is made up of rods and cones. There are more rods in the eye and they are more sensitive to blue light. Rods are responsible for seeing light while the cones are responsible for colors. At night, your eyes are using the rods in order to see and blue light will flood your eyesight decreasing your vision. Hence, the reason for blue-light glasses for heavy use of computers and other devices. 4300K is really the best for both light output and usable light for the eye, but you don't get that pretty bright white look.