I just spent 2 weeks on Kaua’i and it was incredible. Only shot a little over a thousand photos, but I was fortunate enough to have my camera handy one night towards the end of my trip to capture this image:
Moonbows are apparently pretty rare as natural phenomena go, and at first I wasn’t sure exactly what I was seeing. To the naked eye, they appear almost white, and rather faint. But, like normal rainbows, they occur opposite the light source (sun/moon) at an incident angle. We were staying in Poipu beach, not too far from Waimea, which apparently is one of a few spots around the globe that moonbows are known to occur.
Have a peek at the wikipedia article for more info.