This is a pretty big deal in my book. I've seen this one time only, and that was during sunset. I was on the roof of a building in Kaohsiung. I could see the ocean through the surrounding buildings and had heard of this phenomenon, but didn't even know if it was for real. Very cool.

http://www.chinapost.com.tw/taiwan/arts-&-leisure/2015/11/30/452242/Green-flash.htm