I can't say precisely when the great citrus definition diaspora took place in colonies of the Spanish Empire. Spaniards would argue on the side of the limes being green and lemons yellow. Limun being the Persian antecedent to the Medeival Latin lemonium that the famous traveler Christopher Columbus would have used to describe the seeds he brought to Hispaniola in 1492. It is interesting to note that these sorts of shifts in meaning are fairly common (such as cojer, a common verb for grab or get in European Spanish, which has obscene implications in Mexico). Educated purists will continue to point to the Diccionario de la lengua española de la Real Academia Española (Dictionary of the Spanish Language of the Royal Spanish Academy or DRAE), as the authoritative source, which plainly chooses yellow for lemon and green for lime in the common interpretation (less genus and species with unique characteristics producing green lemons, etc.) Either way, of the existing 21 Hispanophonic academies, roughly 17 of them err towards limes being green and lemons yellow, regardless of local tradition in the new world.