I've noticed in certain lights that my fuel filler flap looks a creamier shade of white. But like Craig, I've thought I've imagined it too cos when I look at it again 5 mins later it looks OK.
This is nothing new though. Lots of cars from all sorts of manufacturers have this issue, some much worse than others and it's usually put down to the plastic versus metal and the way light reflects differently off them. The Audi A4 from about 7/8 years ago was particularly bad for this - the lower bumpers / valence were originally unpainted and in a mid-life facelift they painted them, but in lighter metallics they looked a completely wrong shade!