The Poke Ball motifs on the floors of the Pokemon Centers are gold on the top half and silver on the bottom half. This design also appears in the Pal Park.

During a wild Pokemon battle, if the bottom screen is tapped with the DS stylus at certain times before and after the battle options appear, the normally red and white Poke Ball becomes gold and silver colored.

Of course, is pretty much moot, but perhaps on May 10 we'll learn about worldwide release dates and new features for both games. Of course, it's probably safe to assume the game's coming out in America the following season. Nintendo does like to make piles and piles money, after all.