My car failed its MOT last year because the sidelights were the wrong colour. I hadn't ever noticed, but they were a bit blue.
So I took the lights out and had a look (bit of a job to do!!). At some point, the regular halogen (I think) side light bulb that lights up the angel eye ring lens had popped. BMW want around £35 per side for the bulb as it comes integrated into a plastic moulding. So the previous owner had a garage cut up the bulb holder and replace the blown bulb with an LED which had been glued in place. The LED was brighter, but it did look quite blue.
I didn't think it really suited the car either. I like the yellowy light on the sidelights, it suits that era of car. So I coughed up the £70 for two OEM bulbs from BMW and fitted them back into the headlights, so it's all back to stock again now. I did have the old butchered up bulb holders with LEDs glued in somewhere in my garage, but there is a chance I may have thrown them away.