Interesting. I was in Havana at the beginning of the month and went the the 9.00 'closing of the gates' gun re-enactment.? Uniforms of the garrison were white, purple cuffs and pockets, no turn backs or lapels (had a back view, so not be 100% on the latter) with usual black tricorn with white lace edging.? The fortress built after the 1762 invasion is enormous and rather powerfully underlines how important Cuba was to the Spanish treasury. Whether it was ever completed - would have needed a very significant number of guns of medium and large caliber to complete the fit out, not to mention the stores required to maintain the garrison which would have been pretty large too
Before I went, had a quick trawl for info on Spanish SYW uniform info and drew a blank