Here's some info I dug up too on the Sylvania North America website:

"Q) What’s the difference between European and North American SilverStar?

A) The Sylvania North American SilverStar bulbs have a high tech amethyst blue coating to help give the whiter light appearance. The European SilverStar does not have a coating for the whiter light, making it more like the SYLVANIA (US) XtraVision product line. Both bulbs offer
greater luminance (increased brightness)."