2008 ML320 CDI - 119,700 miles
Just recently, within the last 500 miles, the right headlight low beam changed from it's daylight xenon color to a rose color. Is there a reason why and a solution?
Thanks.

The bulb is going bad.

Double check me but I think W164s used OSRAM 66144 bulbs which is a D1S bulb. You can find them online, or autoparts stores can get them,

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68 280SL - 70 280SL - 70 300SEL 3.5 - 72 350SL - 72 280SEL 4.5 - 72 220 - 72 220D - 73 450SL - 84 230GE - 87 200TD - 90 190E 2.0 - 03 G500

Nissan GTR - Nissan Skyline GTS25T - Toyota GTFour - Rover Mini - Toyota Land Cruiser HJ60 - Cadillac Eldorado - BMW E30 - BMW 135i

you can also try moving the bulb to the other side and see if the color changes
with the swap. if it does, then you can conclude the bulb being the cause. i've
also seen color change with the ballast being the culprit (less common).

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-- raymond~
47º 34'N 122º 18'W

More than likely it is the bulb. I recommend changing both bulbs at the same time as xenon bulbs "colour shift" as they age. The new bulb will be significantly brighter and more blue/white compared to an older bulb which is often blue/purple.

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1989 300CE

Thank you all, the advice has been spot on.

Disclaimer: I have some mechanical knowledge which gives me enough confidence in myself to at least look under the hood. I was hesitant to attack replacing the bulb but I got my curiosity up and took a look at what we have. From the time I went into the garage, put on a pair of light duty work gloves, turned the lights on, opened the bonnet, brought a trouble light into play, removed the bulb cover, removed the bulb, and could have replaced it, would not have taken over five minutes, with no hurried frenzy involved. I did take a picture of the Osram 66144 35W base and can now purchase one with confidence.

This was an examination that I have not done before on this vehicle but I did research how to do it, including watching a video of someone with kids band-aids across his knuckles. It is a very straight forward and easy procedure - using tons of caution not to electrocute myself. When I actually do replace the bulb I will use shielding material, probably a couple layers of shop towels in places where needed to prevent metal to metal contact. (Now, in case you are going to ask why I didn't use shielding material this time, it is because as I reviewed what I did I decided it would be a reasonable precaution the next time.) Another tool I will use is an appropriately sized mirror - see below.

I did switch the passenger side rose colored low beam bulb with the other side. Now there is a rose colored bulb on the driver's side and a bright bi-xenon bulb on the passenger side. I am diagnosing that the bulb is failing and that there isn't another electrical issue.

This is the third M-Class we have owned. I had replaced the halogen bulbs in the other two and this replacement is the easiest.

I give the procedure a difficulty rating of 2.5 out of 5. Not because it is that difficult but lots of caution should be taken considering the high voltage. Also, it is impossible to directly see into the bulb socket location so you have to have a nice sense of touch, like an ophthalmologist operating on your optic nerve from inside your head by way of your ear, thus the mirror. And a pair of light, grip infused gloves will help keep the doctor away, and give you a better grip on a Bavarian Dark AFTER the job is done.