What color is the clasp on the pearls? Are they warm or cool in color? If the clasp is gold and/or the pearls warm in color, go with gold. If the clasp is silver and/or the pearls are cool in color, go with silver.

Really it doesn't matter too much, as long as any metal you are wearing matches. The reason I mention the clasps, is because if the necklace slips and it becomes visible, you look good for matching that, as well.