Beyond the bright, sky-blue horizon lies a color richer than royal but less imperial than purple, as seaworthy as navy, as transporting as Aegean, and deeper than swimming pool. It is the one element of the rainbow that everyone forgets about when they're drawing one, but it can't escape mention when reciting the order of colors in the rainbow's yearn-inspiring arc. Indigo is not only the i in ROYGBIV but it's also a brilliantly dark hue with the subtle intensity of sapphires that wonderfully sets off beauty that has been either kissed by the sun or brushed with a blush of pink—and this season it is easier to find than a pot of gold. —Hal Rubenstein