What's on jewelers' wish lists for 2012? Yellow gold, platinum bridal designs, more custom work, and "lots and lots" of colored stones. Oh, plus a little help from the ­economy, thank you very much.Volatile stock markets, high unemployment, and soaring metal costs continued to plague jewelry retailers nationwide in 2011, motivating owners to fine-tune their product assortments in preparation for the new year. JCK informally polled establishments from Maine to California and found that boutique owners watched stones and metals carefully this past year, chose designers prudently, and paid more attention to service, marketing events, and store renovations. Turning the corner into 2012, yellow gold and colored stones showed momentum. In a macroeconomic sense, however, the most significant trend appears to be the widening disparity between middle-of-the-road and affluent consumers. The 1 per