EMERGING MARKETS-Colombian peso, Mexican stocks skyrocket on Fed, oil

(Updates prices, adds Mexico markets, trader quote) By Asher Levine and Jean Luis Arce SAO PAULO/MEXICO CITY, Dec 18 (Reuters) - Colombia's peso closed sharply stronger on Thursday while Mexican stocks posted their biggest gain in over four years as more stable oil prices and reassuring comments by the U.S. Federal Reserve stoked risk appetite. Other Latin American currencies also strengthened after the Fed offered an upbeat assessment of the U.S. economy on Wednesday, helping offse