When I was positioning for Taj Mahal Lego structure in Legoland at Malaysia, a rare scene on the sky appeared. It was a rainbow colored cloud formation and lasted for around 20 mins. I used ND and RGND filters to create a slow motion effect of people and reduce the contrast of the "rainbow effect". I also throw in HDR just in order to maintain the details of all the cloud patterns and especially those mini-figures on the ground.