Already had a thread on this and is often a problem of white on different materials. I had not realised the petrol cap was plastic so sadly there will be a small colour difference. Morenoticeableas the petrol cap is in the middle of a large white area!!
Check it under different lighting conditions and as long as it is only slight is normal I am afraid.
Garage agreed today that mine was wrong colour, are going to either repaint mine or order a new one, repaint it and swap them......I've a candy white cap on a pure white car...doh! Edited by: Privatedoc
from all the posts on this forum, the dealer network seems good. OK, sometimes they need prodding and pointing in the right direction, but on the whole if there is a problem, they eventually agree to sort the problem.