Dorothy would be clicking her heels with glee over the rainbow jewels currently brightening the market. With the robust hues trending in fall ready-to-wear, they’re the perfect way to add color to your world. Whether mixing multicolored sapphires in gradated shades or using an array of gemstones—garnet, citrine, and more—jewelry designers have made it easier than ever to find a rainbow connection.     Magnipheasant Feathers collar in 18k white gold with 145.85 cts. t.w. pavé black diamond, citrine, amethyst, rhodolite, red garnet, blue topaz, peridot, and iolite; $90,000; Stephen Webster, NYC; 212-226-6160; stephenwebster.com Flow collection small four-lines earrings in 18k black gold with 2.2 cts. t.w. colored sappires; $4,650; AS29, Hong Kong; 85-22-530-0529; info@as29.com; as29.com   18k ro