A number of headlamp bulbs have a blue coating on them - Osram Nightbreakers for one.
The high intensity, very white LED bulbs pick this up and give an apparent blueish reflected light.
Unless it's too blue it won't give an MOT problem - I had a long discussion with my local MOT guy about this recently.
If you want pure white sidelights, you have to avoid blue coatings on headlamp bulbs and make sure the LEDs are not exceeding 5k - 6k colour temp. Above that and they are into the 'blue light' spectrum.