For comparison, there are several pics of it from different seasons with different combinations.
My first inclination is white mother of pearl, but perhaps black/smoke MOP or brown horn or something else would make it more versatile and wearable all year and not just in the hot summer. If you have an idea besides one of my poll options, comment with your idea!
(pic courtesy ebw1, who i bought this from a while back)
Warning: Spoiler! (Click to show)