Europe and Japan for some time now, but it hasn't made an appearance in North America as of yet. Well, that's not entirely true: half of the Metallic Silver DS Lite makes up the Guitar Hero: On Tour special edition system. But we never got the back part.
An unspecified "source" has suggested to GoNintendo's RawMeatCowboy that this tragic omission will be corrected this September, with the release of an all-silver DS. That sounds perfectly plausible to us, especially since its partner in shininess, the Metallic Rose, has been released.
It's nice to have such a low-impact rumor so close to E3. We may get a new color, and that would be nice; if not, that's okay too! It's certainly a lot tamer than all those other rumors we've been dealing with.