I did the same on my 335 - however I just went with 5k bulbs.Replacing the bulb with a 'whiter' one is definitely your best bet, as it works as the stock bulb indeed. What you cannot do is put an LED and retain the high beams. I replaced the stock DRL bulb on my M3 (looked like crap stock, very yellow due to the low voltage) with a 'GP Thunders' in 8K temperature (it's just for reference, as those numbers are not right on a bulb like that), and now look pretty white. I might do that on this car too.
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