As to the green flash. Yes it is real and I've seen it on SXM at least once in a week's visit since the late 80's. I stay at the Divi and have a good vantage point during week 11 and it is even better in April when I switch weeks. Must admit that the best ones I've seen were in Hawaii either from the Big Island or Kauai.
A few years ago in SXM a group of newbies, grandparents, parents and kids showed up after checking in near my vantage point and I told them to watch the sun. Half saw it and half didn't, so I told them they didn't drink enough rum punch at check-in. <img src="http://www.traveltalkonline.com/forums/images/graemlins/Wink.gif" alt="" /> So, I guess I helped with the urban myth that only drinkers see it.
It is dependent on a clear sky sunset.