A newer, inkier shade of black rhodium is enabling jewelry designers the world over to explore their dark sides. The heady metal adds drama to of-the-moment styles, gives classic designs a contemporary twist, and creates cool effects when used underneath gems—making light stones pop and enhancing the edginess of dark gems. Talk about black magic!   (Top) Diamond Pyramid bangle in black rhodium–plated 18k gold; $20,000; Sutra, Houston; 713-984-4987; sutrajewels.com   (Inset) Diamond, sapphire, tsavorite, and onyx ring in black rhodium–plated 18k gold; $13,900; Lydia Courteille, Paris; 33-14-261-1171; lydiacourteille.com    Huggie earrings in 14k gold with black rhodium and 0.12 ct. t.w. diamonds; $370; Shy Creation, Los Angeles; 213-623-8900; shycreation.com   Full Moon necklace with labradorite and diamonds in bla