yellow lights are allowed as all fench cars that come over to the uk have them as standard
and they dont have to change over to white or slightly blue bulbs to drive over here my girlfriend had a set of yellow xenon lights on her car for over a year and not one problem and passed the mot with them in
if you looking directly at them e approved yellow bulbs should only have a slight tint its when you view from an angle you see the proper yellowy ness
hope this helps
-si-