When i bought my gt4 the guy i got it off told me it had new alloys on because they were being re-called as that type alloy had a coating fault and wasn't lasting long in the UK !!
He had them re done and they came back the wrong shade so Nissan replaced them free of charge with the correct shade !!
maybe this happened to yours too that's why your new ones are different !??!
like i said the guy told me this so i don't know how true it is !!