IIRC, 1K cards were white some time ago (before 2006, which was the first year I got 1K and had the black-with-gold-flecks card). It does seem a bit weird, though.

As for prior points about why one would need the card, I will say every single *A lounge I visited this past week wanted to see my *G card. They scanned the BP, then asked for the card and swiped it, too. LH lounges at IAD & FRA, BD at EDI, and the *A lounge at LHR. Glad I got my card before the trip...