Now that is a GREEN flash! Watching for them can lead to serious retinal damage. I try to ration my searches, but once having seen that they really occur, it can become an obsession. You have to be very patient, and wait until the disc almost slips below the horizon. Alas, my photographic efforts have never born such 'verdant' fruit, but I will pursue my quixotic search (which will require several more trips to Hawaii and SBH).